move open discussions to other merge request

Description

Sometimes when reviewing a are merge request, reviewers may find issues which cannot be solved in the context of the current merge request. Reason are:

• the issue found only show up while implementing the current task however solving it would require a bigger refactoring which is unrelated to task itself.
• the change on the merge request need to go back now since others waiting for it, cleanup can be done in a second step
• comments completely unrelated

Proposal

There should be a way to move open discussions to other merge requests. Best would be have a list where you can select which one should be moved and select the target merge request or a new merge request where they should be moved.

Note: In a second step it might also make sense to have the ability to move discussions to an issue (is that currently possible) or commit.