Avoid creating unnecessary temporary cat file sub process (#33942)

Extract from #33934 

In the same goroutine, we should reuse the exist cat file sub process
which exist in `git.Repository` to avoid creating a unnecessary
temporary subprocess.

This PR reuse the exist cate file writer and reader in
`getCommitFromBatchReader`.
It also move `prepareLatestCommitInfo` before creating dataRc which will
hold the writer so other git operation will create a temporary cat file
subprocess.

routers/api/v1/repo/tag.go

@@ -110,7 +110,7 @@ func GetAnnotatedTag(ctx *context.APIContext) {
 	if tag, err := ctx.Repo.GitRepo.GetAnnotatedTag(sha); err != nil {
 		ctx.APIError(http.StatusBadRequest, err)
 	} else {
-		commit, err := tag.Commit(ctx.Repo.GitRepo)
+		commit, err := ctx.Repo.GitRepo.GetTagCommit(tag.Name)
 		if err != nil {
 			ctx.APIError(http.StatusBadRequest, err)
 		}