Also sync DB branches on push if necessary (#28361) (#28403)

Fix #28056
Backport #28361 

This PR will check whether the repo has zero branch when pushing a
branch. If that, it means this repository hasn't been synced.

The reason caused that is after user upgrade from v1.20 -> v1.21, he
just push branches without visit the repository user interface. Because
all repositories routers will check whether a branches sync is necessary
but push has not such check.

For every repository, it has two states, synced or not synced. If there
is zero branch for a repository, then it will be assumed as non-sync
state. Otherwise, it's synced state. So if we think it's synced, we just
need to update branch/insert new branch. Otherwise do a full sync. So
that, for every push, there will be almost no extra load added. It's
high performance than yours.

For the implementation, we in fact will try to update the branch first,
if updated success with affect records > 0, then all are done. Because
that means the branch has been in the database. If no record is
affected, that means the branch does not exist in database. So there are
two possibilities. One is this is a new branch, then we just need to
insert the record. Another is the branches haven't been synced, then we
need to sync all the branches into database.

1 files changed, 2 insertions, 3 deletions

diff --git a/routers/api/v1/repo/branch.go b/routers/api/v1/repo/branch.go
index c851525c0f..922f15f749 100644
--- a/routers/api/v1/repo/branch.go
+++ b/routers/api/v1/repo/branch.go
@@ -262,12 +262,11 @@ func CreateBranch(ctx *context.APIContext) {
 		}
 	}
 
-	err = repo_service.CreateNewBranchFromCommit(ctx, ctx.Doer, ctx.Repo.Repository, oldCommit.ID.String(), opt.BranchName)
+	err = repo_service.CreateNewBranchFromCommit(ctx, ctx.Doer, ctx.Repo.Repository, ctx.Repo.GitRepo, oldCommit.ID.String(), opt.BranchName)
 	if err != nil {
 		if git_model.IsErrBranchNotExist(err) {
 			ctx.Error(http.StatusNotFound, "", "The old branch does not exist")
-		}
-		if models.IsErrTagAlreadyExists(err) {
+		} else if models.IsErrTagAlreadyExists(err) {
 			ctx.Error(http.StatusConflict, "", "The branch with the same tag already exists.")
 		} else if git_model.IsErrBranchAlreadyExists(err) || git.IsErrPushOutOfDate(err) {
 			ctx.Error(http.StatusConflict, "", "The branch already exists.")