Allow multiple open merge requests from same source and target branch

Problem to solve

There is a current limitation within GitLab preventing multiple open Merge Requests from the same source branch. In many cases it doesn't make sense to allow multiple MRs from the same source since both would be attempts at merging the same commits, however as a product, GitLab provides a lot of functionality on top of Source Control that could benefit from separation.

Intended users

Persona: Software developer

Possible usecases

As a user, I want to keep reviews and discussions on the same code diff separate and isolated between teams

Further details

Proposal

Remove validation preventing the opening of multiple MRs from a given source branch

Permissions and Security

No change to existing MR permissions

Documentation

Testing

What does success look like, and how can we measure that?

Users are allowed to open multiple MRs to separate discussion or dismissal from a given source branch.

Links / references

Edited by Lucas Charles