Add loading yaml label template files (#22976) (#23232)

Backport #22976

Extract from #11669 and enhancement to #22585 to support exclusive
scoped labels in label templates

* Move label template functionality to label module
* Fix handling of color codes
* Add Advanced label template

Co-authored-by: Lauris BH <lauris@nix.lv>

modules/options/repo.go

@@ -0,0 +1,44 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package options
+
+import (
+	"fmt"
+	"os"
+	"path"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/util"
+)
+
+// GetRepoInitFile returns repository init files
+func GetRepoInitFile(tp, name string) ([]byte, error) {
+	cleanedName := strings.TrimLeft(path.Clean("/"+name), "/")
+	relPath := path.Join("options", tp, cleanedName)
+
+	// Use custom file when available.
+	customPath := path.Join(setting.CustomPath, relPath)
+	isFile, err := util.IsFile(customPath)
+	if err != nil {
+		log.Error("Unable to check if %s is a file. Error: %v", customPath, err)
+	}
+	if isFile {
+		return os.ReadFile(customPath)
+	}
+
+	switch tp {
+	case "readme":
+		return Readme(cleanedName)
+	case "gitignore":
+		return Gitignore(cleanedName)
+	case "license":
+		return License(cleanedName)
+	case "label":
+		return Labels(cleanedName)
+	default:
+		return []byte{}, fmt.Errorf("Invalid init file type")
+	}
+}