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

i18n/en.json

@@ -3854,6 +3854,10 @@
     "id": "app.plugin.deactivate.app_error",
     "translation": "Unable to deactivate plugin"
   },
+  {
+    "id": "app.plugin.delete_plugin_status_state.app_error",
+    "translation": "Unable to delete plugin status state."
+  },
   {
     "id": "app.plugin.disabled.app_error",
     "translation": "Plugins have been disabled. Please check your logs for details."
@@ -3898,10 +3902,18 @@
     "id": "app.plugin.not_installed.app_error",
     "translation": "Plugin is not installed"
   },
+  {
+    "id": "app.plugin.prepackaged.app_error",
+    "translation": "Cannot install prepackaged plugin"
+  },
   {
     "id": "app.plugin.remove.app_error",
     "translation": "Unable to delete plugin"
   },
+  {
+    "id": "app.plugin.set_plugin_status_state.app_error",
+    "translation": "Unable to set plugin status state."
+  },
   {
     "id": "app.plugin.upload_disabled.app_error",
     "translation": "Plugins and/or plugin uploads have been disabled."
@@ -4798,6 +4810,10 @@
     "id": "model.client.writer.app_error",
     "translation": "Unable to build multipart request"
   },
+  {
+    "id": "model.cluster.is_valid.id.app_error",
+    "translation": "Invalid Id"
+  },
   {
     "id": "model.command.is_valid.create_at.app_error",
     "translation": "Create at must be a valid time"