Edit files even if related to a specific commit

Description

When you are viewing a file that is related to a specific commit instead of a branch, you cannot edit it:

This is breaking a flow that could be useful when fixing security problems.

1. users read the security report in the MR
2. they click on the link, reaching the file/line that caused the error
3. they want to fix it by editing the file and committing the change

Proposal

Allow users to edit the file even if it is related to a specific commit. They will be asked to pick up a branch where the new changes will be pushed.