[API] Migration: Change ServiceType String (#12672)

* use different structs for MigrateRepoOptions on UI and API

* Fix TokenAuth and rename UID to an understandable Name

* fix swagger doc

* simplify & mk redable

* R E F A C T O R:
migration has now internal 3 structs to store its options:
 * the Options for WebUI: modules/auth/repo_form.go
 * the Options for API: modules/structs/repo.go
 * the option struct with after validation for internal prossessing: modules/migrations/base/options.go

* Copyright Header

* Deprecate UID - add RepoOwner

* adopt repo.go -> migrate.go

* add comment about each struct purpose

* lint

modules/convert/utils.go

@@ -1,3 +1,4 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
 // Copyright 2016 The Gogs Authors. All rights reserved.
 // Use of this source code is governed by a MIT-style
 // license that can be found in the LICENSE file.
@@ -5,7 +6,10 @@
 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.
@@ -17,3 +21,19 @@ func ToCorrectPageSize(size int) int {
 	}
 	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
+	default:
+		return structs.PlainGitService
+	}
+}