Move convert package to services (#22264)

Addition to #22256

The `convert` package relies heavily on different models which is
[disallowed by our definition of
modules](https://github.com/go-gitea/gitea/blob/main/CONTRIBUTING.md#design-guideline).
This helps to prevent possible import cycles.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

services/convert/utils.go

@@ -0,0 +1,42 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Copyright 2016 The Gogs Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package convert
+
+import (
+	"strings"
+
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/structs"
+)
+
+// ToCorrectPageSize makes sure page size is in allowed range.
+func ToCorrectPageSize(size int) int {
+	if size <= 0 {
+		size = setting.API.DefaultPagingNum
+	} else if size > setting.API.MaxResponseItems {
+		size = setting.API.MaxResponseItems
+	}
+	return size
+}
+
+// ToGitServiceType return GitServiceType based on string
+func ToGitServiceType(value string) structs.GitServiceType {
+	switch strings.ToLower(value) {
+	case "github":
+		return structs.GithubService
+	case "gitea":
+		return structs.GiteaService
+	case "gitlab":
+		return structs.GitlabService
+	case "gogs":
+		return structs.GogsService
+	case "onedev":
+		return structs.OneDevService
+	case "gitbucket":
+		return structs.GitBucketService
+	default:
+		return structs.PlainGitService
+	}
+}