Some refactors for issues stats (#24793)

This PR

- [x] Move some functions from `issues.go` to `issue_stats.go` and
`issue_label.go`
- [x] Remove duplicated issue options `UserIssueStatsOption` to keep
only one `IssuesOptions`

modules/indexer/issues/indexer.go

@@ -302,7 +302,7 @@ func populateIssueIndexer(ctx context.Context) {
 // UpdateRepoIndexer add/update all issues of the repositories
 func UpdateRepoIndexer(ctx context.Context, repo *repo_model.Repository) {
 	is, err := issues_model.Issues(ctx, &issues_model.IssuesOptions{
-		RepoID:   repo.ID,
+		RepoIDs:  []int64{repo.ID},
 		IsClosed: util.OptionalBoolNone,
 		IsPull:   util.OptionalBoolNone,
 	})