Allow detect whether it's in a database transaction for a context.Context (#21756)

Fix #19513

This PR introduce a new db method `InTransaction(context.Context)`,
and also builtin check on `db.TxContext` and `db.WithTx`.
There is also a new method `db.AutoTx` has been introduced but could be used by other PRs.

`WithTx` will always open a new transaction, if a transaction exist in context, return an error.
`AutoTx` will try to open a new transaction if no transaction exist in context.
That means it will always enter a transaction if there is no error.

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: 6543 <6543@obermui.de>

services/org/repo.go

@@ -22,7 +22,7 @@ func TeamAddRepository(t *organization.Team, repo *repo_model.Repository) (err e
 		return nil
 	}
 
-	return db.WithTx(func(ctx context.Context) error {
+	return db.WithTx(db.DefaultContext, func(ctx context.Context) error {
 		return models.AddRepository(ctx, t, repo)
 	})
 }