Split migrations folder (#21549)

There are too many files in `models/migrations` folder so that I split
them into sub folders.

models/migrations/v1_16/v195.go

@@ -0,0 +1,47 @@
+// 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 v1_16 //nolint
+
+import (
+	"fmt"
+
+	"xorm.io/xorm"
+)
+
+func AddTableCommitStatusIndex(x *xorm.Engine) error {
+	// CommitStatusIndex represents a table for commit status index
+	type CommitStatusIndex struct {
+		ID       int64
+		RepoID   int64  `xorm:"unique(repo_sha)"`
+		SHA      string `xorm:"unique(repo_sha)"`
+		MaxIndex int64  `xorm:"index"`
+	}
+
+	if err := x.Sync2(new(CommitStatusIndex)); err != nil {
+		return fmt.Errorf("Sync2: %w", err)
+	}
+
+	sess := x.NewSession()
+	defer sess.Close()
+
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	// Remove data we're goint to rebuild
+	if _, err := sess.Table("commit_status_index").Where("1=1").Delete(&CommitStatusIndex{}); err != nil {
+		return err
+	}
+
+	// Create current data for all repositories with issues and PRs
+	if _, err := sess.Exec("INSERT INTO commit_status_index (repo_id, sha, max_index) " +
+		"SELECT max_data.repo_id, max_data.sha, max_data.max_index " +
+		"FROM ( SELECT commit_status.repo_id AS repo_id, commit_status.sha AS sha, max(commit_status.`index`) AS max_index " +
+		"FROM commit_status GROUP BY commit_status.repo_id, commit_status.sha) AS max_data"); err != nil {
+		return err
+	}
+
+	return sess.Commit()
+}