Implement v4 endpoints for OAuth (#6040)

* Implement POST /oauth/apps endpoint for APIv4

* Implement GET /oauth/apps endpoint for APIv4

* Implement GET /oauth/apps/{app_id} and /oauth/apps/{app_id}/info endpoints for APIv4

* Refactor API version independent oauth endpoints

* Implement DELETE /oauth/apps/{app_id} endpoint for APIv4

* Implement /oauth/apps/{app_id}/regen_secret endpoint for APIv4

* Implement GET /user/{user_id}/oauth/apps/authorized endpoint for APIv4

* Implement POST /oauth/deauthorize endpoint

api/apitestlib.go

@@ -75,6 +75,7 @@ func Setup() *TestHelper {
 		InitRouter()
 		wsapi.InitRouter()
 		app.StartServer()
+		api4.InitApi(false)
 		InitApi()
 		wsapi.InitApi()
 		utils.EnableDebugLogForTest()