MM-8622: Improved plugin error reporting (#8737)

* allow `Wait()`ing on the supervisor

In the event the plugin supervisor shuts down a plugin for crashing too
many times, the new `Wait()` interface allows the `ActivatePlugin` to
accept a callback function to trigger when `supervisor.Wait()` returns.
If the supervisor shuts down normally, this callback is invoked with
a nil error, otherwise any error reported by the supervisor is passed
along.

* improve plugin activation/deactivation logic

Avoid triggering activation of previously failed-to-start plugins just
becase something in the configuration changed. Now, intelligently
compare the global enable bit as well as the each individual plugin's
enabled bit.

* expose store to manipulate PluginStatuses

* expose API to fetch plugin statuses

* keep track of whether or not plugin sandboxing is supported

* transition plugin statuses

* restore error on plugin activation if already active

* don't initialize test plugins until successfully loaded

* emit websocket events when plugin statuses change

* skip pruning if already initialized

* MM-8622: maintain plugin statuses in memory

Switch away from persisting plugin statuses to the database, and
maintain in memory instead. This will be followed by a cluster interface
to query the in-memory status of plugin statuses from all cluster nodes.

At the same time, rename `cluster_discovery_id` on the `PluginStatus`
model object to `cluster_id`.

* MM-8622: aggregate plugin statuses across cluster

* fetch cluster plugin statuses when emitting websocket notification

* address unit test fixes after rebasing

* relax (poor) racey unit test re: supervisor.Wait()

* make store-mocks

1 files changed, 39 insertions, 38 deletions

diff --git a/model/websocket_message.go b/model/websocket_message.go
index 08c238480..071975d6c 100644
--- a/model/websocket_message.go
+++ b/model/websocket_message.go
@@ -10,44 +10,45 @@ import (
 )
 
 const (
-	WEBSOCKET_EVENT_TYPING                 = "typing"
-	WEBSOCKET_EVENT_POSTED                 = "posted"
-	WEBSOCKET_EVENT_POST_EDITED            = "post_edited"
-	WEBSOCKET_EVENT_POST_DELETED           = "post_deleted"
-	WEBSOCKET_EVENT_CHANNEL_DELETED        = "channel_deleted"
-	WEBSOCKET_EVENT_CHANNEL_CREATED        = "channel_created"
-	WEBSOCKET_EVENT_CHANNEL_UPDATED        = "channel_updated"
-	WEBSOCKET_EVENT_CHANNEL_MEMBER_UPDATED = "channel_member_updated"
-	WEBSOCKET_EVENT_DIRECT_ADDED           = "direct_added"
-	WEBSOCKET_EVENT_GROUP_ADDED            = "group_added"
-	WEBSOCKET_EVENT_NEW_USER               = "new_user"
-	WEBSOCKET_EVENT_ADDED_TO_TEAM          = "added_to_team"
-	WEBSOCKET_EVENT_LEAVE_TEAM             = "leave_team"
-	WEBSOCKET_EVENT_UPDATE_TEAM            = "update_team"
-	WEBSOCKET_EVENT_DELETE_TEAM            = "delete_team"
-	WEBSOCKET_EVENT_USER_ADDED             = "user_added"
-	WEBSOCKET_EVENT_USER_UPDATED           = "user_updated"
-	WEBSOCKET_EVENT_USER_ROLE_UPDATED      = "user_role_updated"
-	WEBSOCKET_EVENT_MEMBERROLE_UPDATED     = "memberrole_updated"
-	WEBSOCKET_EVENT_USER_REMOVED           = "user_removed"
-	WEBSOCKET_EVENT_PREFERENCE_CHANGED     = "preference_changed"
-	WEBSOCKET_EVENT_PREFERENCES_CHANGED    = "preferences_changed"
-	WEBSOCKET_EVENT_PREFERENCES_DELETED    = "preferences_deleted"
-	WEBSOCKET_EVENT_EPHEMERAL_MESSAGE      = "ephemeral_message"
-	WEBSOCKET_EVENT_STATUS_CHANGE          = "status_change"
-	WEBSOCKET_EVENT_HELLO                  = "hello"
-	WEBSOCKET_EVENT_WEBRTC                 = "webrtc"
-	WEBSOCKET_AUTHENTICATION_CHALLENGE     = "authentication_challenge"
-	WEBSOCKET_EVENT_REACTION_ADDED         = "reaction_added"
-	WEBSOCKET_EVENT_REACTION_REMOVED       = "reaction_removed"
-	WEBSOCKET_EVENT_RESPONSE               = "response"
-	WEBSOCKET_EVENT_EMOJI_ADDED            = "emoji_added"
-	WEBSOCKET_EVENT_CHANNEL_VIEWED         = "channel_viewed"
-	WEBSOCKET_EVENT_PLUGIN_ACTIVATED       = "plugin_activated"   // EXPERIMENTAL - SUBJECT TO CHANGE
-	WEBSOCKET_EVENT_PLUGIN_DEACTIVATED     = "plugin_deactivated" // EXPERIMENTAL - SUBJECT TO CHANGE
-	WEBSOCKET_EVENT_ROLE_UPDATED           = "role_updated"
-	WEBSOCKET_EVENT_LICENSE_CHANGED        = "license_changed"
-	WEBSOCKET_EVENT_CONFIG_CHANGED         = "config_changed"
+	WEBSOCKET_EVENT_TYPING                  = "typing"
+	WEBSOCKET_EVENT_POSTED                  = "posted"
+	WEBSOCKET_EVENT_POST_EDITED             = "post_edited"
+	WEBSOCKET_EVENT_POST_DELETED            = "post_deleted"
+	WEBSOCKET_EVENT_CHANNEL_DELETED         = "channel_deleted"
+	WEBSOCKET_EVENT_CHANNEL_CREATED         = "channel_created"
+	WEBSOCKET_EVENT_CHANNEL_UPDATED         = "channel_updated"
+	WEBSOCKET_EVENT_CHANNEL_MEMBER_UPDATED  = "channel_member_updated"
+	WEBSOCKET_EVENT_DIRECT_ADDED            = "direct_added"
+	WEBSOCKET_EVENT_GROUP_ADDED             = "group_added"
+	WEBSOCKET_EVENT_NEW_USER                = "new_user"
+	WEBSOCKET_EVENT_ADDED_TO_TEAM           = "added_to_team"
+	WEBSOCKET_EVENT_LEAVE_TEAM              = "leave_team"
+	WEBSOCKET_EVENT_UPDATE_TEAM             = "update_team"
+	WEBSOCKET_EVENT_DELETE_TEAM             = "delete_team"
+	WEBSOCKET_EVENT_USER_ADDED              = "user_added"
+	WEBSOCKET_EVENT_USER_UPDATED            = "user_updated"
+	WEBSOCKET_EVENT_USER_ROLE_UPDATED       = "user_role_updated"
+	WEBSOCKET_EVENT_MEMBERROLE_UPDATED      = "memberrole_updated"
+	WEBSOCKET_EVENT_USER_REMOVED            = "user_removed"
+	WEBSOCKET_EVENT_PREFERENCE_CHANGED      = "preference_changed"
+	WEBSOCKET_EVENT_PREFERENCES_CHANGED     = "preferences_changed"
+	WEBSOCKET_EVENT_PREFERENCES_DELETED     = "preferences_deleted"
+	WEBSOCKET_EVENT_EPHEMERAL_MESSAGE       = "ephemeral_message"
+	WEBSOCKET_EVENT_STATUS_CHANGE           = "status_change"
+	WEBSOCKET_EVENT_HELLO                   = "hello"
+	WEBSOCKET_EVENT_WEBRTC                  = "webrtc"
+	WEBSOCKET_AUTHENTICATION_CHALLENGE      = "authentication_challenge"
+	WEBSOCKET_EVENT_REACTION_ADDED          = "reaction_added"
+	WEBSOCKET_EVENT_REACTION_REMOVED        = "reaction_removed"
+	WEBSOCKET_EVENT_RESPONSE                = "response"
+	WEBSOCKET_EVENT_EMOJI_ADDED             = "emoji_added"
+	WEBSOCKET_EVENT_CHANNEL_VIEWED          = "channel_viewed"
+	WEBSOCKET_EVENT_PLUGIN_ACTIVATED        = "plugin_activated"        // EXPERIMENTAL - SUBJECT TO CHANGE
+	WEBSOCKET_EVENT_PLUGIN_DEACTIVATED      = "plugin_deactivated"      // EXPERIMENTAL - SUBJECT TO CHANGE
+	WEBSOCKET_EVENT_PLUGIN_STATUSES_CHANGED = "plugin_statuses_changed" // EXPERIMENTAL - SUBJECT TO CHANGE
+	WEBSOCKET_EVENT_ROLE_UPDATED            = "role_updated"
+	WEBSOCKET_EVENT_LICENSE_CHANGED         = "license_changed"
+	WEBSOCKET_EVENT_CONFIG_CHANGED          = "config_changed"
 )
 
 type WebSocketMessage interface {