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/repository/repository.go

@@ -90,7 +90,7 @@ func Init() error {
 
 // UpdateRepository updates a repository
 func UpdateRepository(repo *repo_model.Repository, visibilityChanged bool) (err error) {
-	ctx, committer, err := db.TxContext()
+	ctx, committer, err := db.TxContext(db.DefaultContext)
 	if err != nil {
 		return err
 	}