Option to define branch, repo and commit message.

Currently the repo and branch are statically defined. Add the option to define the branch and repo in the synch process. I would like to have the option in the Frontend that after clicking a button like synch to gitlab a modal dialog appears which asks which branch should be used.

Therefore, it is necessary to adapt the endpoint in the backend. However, I would say that the information which branch, which repo is not mandatory in the request. Overall, the default branch and repo should be the same like today.

Lastly the endpoint should support passing a commit message which should be used. Like above, have a default commit message if nothing is entered.