Move git config/remote to gitrepo package and add global lock to resolve possible conflict when updating repository git config file (#35151)

Partially fix #32018 

`git config` and `git remote` write operations create a temporary file
named `config.lock`. Since these operations are not atomic, they must
not be run in parallel. If two requests attempt to modify the same
repository concurrently—such as during a compare operation—one may fail
due to the presence of an existing `config.lock` file.

In cases where `config.lock` is left behind due to an unexpected program
exit, a global lock mechanism could allow us to safely remove the stale
lock file when a related error is detected. While this behavior is not
yet implemented in this PR, it is planned for a future enhancement.

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/compare.go

@@ -41,6 +41,7 @@ import (
 	"code.gitea.io/gitea/services/context"
 	"code.gitea.io/gitea/services/context/upload"
 	"code.gitea.io/gitea/services/gitdiff"
+	pull_service "code.gitea.io/gitea/services/pull"
 )
 
 const (
@@ -550,7 +551,7 @@ func ParseCompareInfo(ctx *context.Context) *common.CompareInfo {
 		headBranchRef = git.TagPrefix + ci.HeadBranch
 	}
 
-	ci.CompareInfo, err = ci.HeadGitRepo.GetCompareInfo(baseRepo.RepoPath(), baseBranchRef, headBranchRef, ci.DirectComparison, fileOnly)
+	ci.CompareInfo, err = pull_service.GetCompareInfo(ctx, baseRepo, ci.HeadRepo, ci.HeadGitRepo, baseBranchRef, headBranchRef, ci.DirectComparison, fileOnly)
 	if err != nil {
 		ctx.ServerError("GetCompareInfo", err)
 		return nil