Sync branches into databases (#22743)

Related #14180
Related #25233 
Related #22639
Close #19786
Related #12763 

This PR will change all the branches retrieve method from reading git
data to read database to reduce git read operations.

- [x] Sync git branches information into database when push git data
- [x] Create a new table `Branch`, merge some columns of `DeletedBranch`
into `Branch` table and drop the table `DeletedBranch`.
- [x] Read `Branch` table when visit `code` -> `branch` page
- [x] Read `Branch` table when list branch names in `code` page dropdown
- [x] Read `Branch` table when list git ref compare page
- [x] Provide a button in admin page to manually sync all branches.
- [x] Sync branches if repository is not empty but database branches are
empty when visiting pages with branches list
- [x] Use `commit_time desc` as the default FindBranch order by to keep
consistent as before and deleted branches will be always at the end.

---------

Co-authored-by: Jason Song <i@wolfogre.com>

models/fixtures/branch.yml

@@ -0,0 +1,47 @@
+-
+  id: 1
+  repo_id: 1
+  name: 'foo'
+  commit_id: '65f1bf27bc3bf70f64657658635e66094edbcb4d'
+  commit_message: 'first commit'
+  commit_time: 978307100
+  pusher_id: 1
+  is_deleted: true
+  deleted_by_id: 1
+  deleted_unix: 978307200
+
+-
+  id: 2
+  repo_id: 1
+  name: 'bar'
+  commit_id: '62fb502a7172d4453f0322a2cc85bddffa57f07a'
+  commit_message: 'second commit'
+  commit_time: 978307100
+  pusher_id: 1
+  is_deleted: true
+  deleted_by_id: 99
+  deleted_unix: 978307200
+
+-
+  id: 3
+  repo_id: 1
+  name: 'branch2'
+  commit_id: '985f0301dba5e7b34be866819cd15ad3d8f508ee'
+  commit_message: 'make pull5 outdated'
+  commit_time: 1579166279
+  pusher_id: 1
+  is_deleted: false
+  deleted_by_id: 0
+  deleted_unix: 0
+
+-
+  id: 4
+  repo_id: 1
+  name: 'master'
+  commit_id: '65f1bf27bc3bf70f64657658635e66094edbcb4d'
+  commit_message: 'Initial commit'
+  commit_time: 1489927679
+  pusher_id: 1
+  is_deleted: false
+  deleted_by_id: 0
+  deleted_unix: 0

models/fixtures/deleted_branch.yml

@@ -1,15 +0,0 @@
--
-  id: 1
-  repo_id: 1
-  name: foo
-  commit: 1213212312313213213132131
-  deleted_by_id: 1
-  deleted_unix: 978307200
-
--
-  id: 2
-  repo_id: 1
-  name: bar
-  commit: 5655464564554545466464655
-  deleted_by_id: 99
-  deleted_unix: 978307200