merge_request push options without .create should update the url returned by Gitlab
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### Release notes
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### Problem to solve
When using the `merge_request.target=<target>` push option without also giving `merge_request.creat`, Gitlab replies with the following error:
```
remote: ========================================================================
remote:
remote: WARNINGS: Error encountered with push options
remote: 'merge_request.target=<target>': A merge_request.create push option
remote: is required to create a merge request for branch
remote: <source>
remote:
remote: ========================================================================
remote:
remote: To create a merge request for <source>, visit:
remote: https://gitlab.com/<project>/-/merge_requests/new?merge_request%5Bsource_branch%5D=<source>
remote:
```
This is very clear, but it could also provide a link with the target branch already set. And simplify creating the merge request via the URL.
### Proposal
Using `merge_request.*` push options should work without `merge_request.create` and update the URL.
```bash
$ git push -o merge_request.target=<target> origin <source>
remote:
remote: To create a merge request for <source> visit:
remote: https://gitlab.com/<project>/-/merge_requests/new?merge_request%5Bsource_branch%5D=<source>&merge_request%5Btarget_branch%5B=<target>
remote:
```
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issue