Add support of Gitlab multi-branch pipeline

Created by: LinuxSuRen

What would you like to be added: It will be a new option for creating a multi-branch pipeline. What we need are the red fields of the below picture.

Gitlab multi-branch pipeline also needs a git tag discover feature. About this part, you can check out https://github.com/kubesphere/console/issues/1310

Why is this needed: Gitlab is a very popular git provider. Many users want to have this feature.

How to test against it Please check out the below issue if you need the backend to test it. You can give all details of the backend. https://github.com/kubesphere/kubesphere/pull/3131