Keep co-authorship when edititing commit message when applying suggestions
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### Release notes
Better recognise contributors' contributions by capturing co-authorship even if the commit message is changed when applying suggestions.
### Problem to solve
If a number of contributors leave suggestions on a merge request and they are added to batch. I have two options:
- Add a really non-descriptive commit message "Applying 3 suggestions to 2 files" with co-authorship
- Add my own commit message, but the co-authorship disappears
I can manually add co-authorship back, but this takes time and involves double checking who submitted suggestions, and then getting their email and writing it in the correct format.
### Intended users
_Sorry, I didn't read all of the personas!_
*Main user:*
Users accepting suggestions with clear commit messages.
*Main beneficiary*:
### User experience goal
This improves user experience for two main groups:
- **Users accepting suggestions** - Saving them time not manually re-adding attribution of co-authorship,
- **Contributors making suggestions** - Attribution of co-authorship can be meaningful especially to new contributors. This tends to get deleted if people are not aware that it isn't automatically appended.
### Proposal
When you start typing a commit message now it deletes the entire auto-generated message. It would be good to delete the `applying N suggestions to M files` but keep the co-authorship lines.
### Further details
None
### Permissions and Security
Shouldn't have any security implications
### Documentation
I believe this would be expected behaviour, so I don't believe it would need extra documentation?
### Availability & Testing
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### Available Tier
Free please :angel:
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### Feature Usage Metrics
If you really wanted to track it, you could see if co-authorship messages increase.
### What does success look like, and how can we measure that?
Happy new contributors being accepted.
### What is the type of buyer?
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### Is this a cross-stage feature?
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### What is the competitive advantage or differentiation for this feature?
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