MM-53355: tidy up plugins (#24194)

* remove feature flag managed plugins

* remove unneeded plugin blocklist

* remove unnecessary wrappers

* documentation and logging improvements

* avoid use of global logger
* leverage wrapped loggers (e.g. consistently log `plugin_id`)
* promote some logs from `Debug` to `Info` for better visibility.
* extract installPluginToFilestore
* rename some variables for consistency / clarity

* make generated

server/i18n/en.json

@@ -6023,10 +6023,6 @@
     "id": "app.oauth.update_app.updating.app_error",
     "translation": "We encountered an error updating the app."
   },
-  {
-    "id": "app.plugin.blocked.app_error",
-    "translation": "Plugin {{.Id}} is on the block list. Some plugins are blocked because they are built into this version of Mattermost."
-  },
   {
     "id": "app.plugin.cluster.save_config.app_error",
     "translation": "The plugin configuration in your config.json file must be updated manually when using ReadOnlyConfig with clustering enabled."