MM-10249 Adding plugin ability to intercept posts before they reach the DB. (#8791)

* Adding plugin ability to intercept posts before they reach the DB.

* s/envoked/invoked/

app/plugin.go

@@ -661,3 +661,7 @@ func (a *App) ExecutePluginCommand(args *model.CommandArgs) (*model.Command, *mo
 	}
 	return nil, nil, nil
 }
+
+func (a *App) PluginsReady() bool {
+	return a.PluginEnv != nil && *a.Config().PluginSettings.Enable
+}