Enable to AI plugin by default (#28770)

* Enable to AI plugin by default

* Fix tests.

server/public/model/plugin_constants.go

@@ -10,4 +10,5 @@ const (
 	PluginIdCalls         = "com.mattermost.calls"
 	PluginIdNPS           = "com.mattermost.nps"
 	PluginIdChannelExport = "com.mattermost.plugin-channel-export"
+	PluginIdAI            = "mattermost-ai"
 )