Refactor auth middleware (#36848)

Principles: let the caller decide what it needs, but not let the
framework (middleware) guess what it should do.

Then a lot of hacky code can be removed. And some FIXMEs can be fixed.

This PR introduces a new kind of middleware: "PreMiddleware", it will be
executed before all other middlewares on the same routing level, then a
route can declare its options for other middlewares.

By the way, allow the workflow badge to be accessed by Basic or OAuth2
auth.

Fixes: https://github.com/go-gitea/gitea/pull/36830
Fixes: https://github.com/go-gitea/gitea/issues/36859

routers/init.go

@@ -180,8 +180,9 @@ func InitWebInstalled(ctx context.Context) {
 // NormalRoutes represents non install routes
 func NormalRoutes() *web.Router {
 	r := web.NewRouter()
-	r.Use(common.ProtocolMiddlewares()...)
-	r.Use(common.MaintenanceModeHandler())
+	r.BeforeRouting(common.ProtocolMiddlewares()...)
+
+	r.AfterRouting(common.MaintenanceModeHandler())
 
 	r.Mount("/", web_routers.Routes())
 	r.Mount("/api/v1", apiv1.Routes())