Plugins: Unifying alpha state & options for all plugins (#16530)

* app pages

* app pages

* workign example

* started alpha support

* remove app stuff

* show warning on alpha/beta panels

* put app back on plugin file

* fix go

* add enum for PluginType and PluginIncludeType

* Refactoring and moving settings to plugins section

fixes #16529

pkg/api/plugins.go

@@ -39,7 +39,7 @@ func (hs *HTTPServer) GetPluginList(c *m.ReqContext) Response {
 			continue
 		}
 
-		if pluginDef.State == plugins.PluginStateAlpha && !hs.Cfg.EnableAlphaPanels {
+		if pluginDef.State == plugins.PluginStateAlpha && !hs.Cfg.PluginsEnableAlpha {
 			continue
 		}