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/common/compare.go

@@ -7,6 +7,7 @@ import (
 	repo_model "code.gitea.io/gitea/models/repo"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/git"
+	pull_service "code.gitea.io/gitea/services/pull"
 )
 
 // CompareInfo represents the collected results from ParseCompareInfo
@@ -14,7 +15,7 @@ type CompareInfo struct {
 	HeadUser         *user_model.User
 	HeadRepo         *repo_model.Repository
 	HeadGitRepo      *git.Repository
-	CompareInfo      *git.CompareInfo
+	CompareInfo      *pull_service.CompareInfo
 	BaseBranch       string
 	HeadBranch       string
 	DirectComparison bool