Always use first commit message as default MR title
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=214023)
</details>
<!--IssueSummary end-->
### Problem to solve
Our team has these naming convention:
- branch name: `TEST-1234_branch-name`
- commmit message: `[TEST-1234]: Branch name`
We faced an issue with MR titles.
When branch has only one commit new MR creating with title equals to commit message:
`[TEST-1234]: Branch name`
When branch has two or more commits new MR creating title with modified branch name:
`Test 1234 branch name`
### Intended users
Developers.
### Proposal
Add option in `Settings > General > Merge Requests` to always use first commit message as MR title as default one.
issue