Clean-up HookPreReceive and restore functionality for pushing non-standard refs (#16705)

* Clean-up HookPreReceive and restore functionality for pushing non-standard refs

There was an inadvertent breaking change in #15629 meaning that notes refs and other
git extension refs will be automatically rejected.

Further following #14295 and #15629 the pre-recieve hook code is untenably long and
too complex.

This PR refactors the hook code and removes the incorrect forced rejection of
non-standard refs.

Fix #16688

Signed-off-by: Andrew Thornton <art27@cantab.net>

routers/private/hook_proc_receive.go

@@ -0,0 +1,34 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+// Package private includes all internal routes. The package name internal is ideal but Golang is not allowed, so we use private as package name instead.
+package private
+
+import (
+	"net/http"
+
+	gitea_context "code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/private"
+	"code.gitea.io/gitea/modules/web"
+	"code.gitea.io/gitea/services/agit"
+)
+
+// HookProcReceive proc-receive hook - only handles agit Proc-Receive requests at present
+func HookProcReceive(ctx *gitea_context.PrivateContext) {
+	opts := web.GetForm(ctx).(*private.HookOptions)
+	if !git.SupportProcReceive {
+		ctx.Status(http.StatusNotFound)
+		return
+	}
+
+	results := agit.ProcRecive(ctx, opts)
+	if ctx.Written() {
+		return
+	}
+
+	ctx.JSON(http.StatusOK, private.HookProcReceiveResult{
+		Results: results,
+	})
+}