Add re-blaming functionality to blame view

Problem to solve

It would be useful to be able to retrieve the blame for a line of code prior to the most recent blame. This is a native feature of Github's UI and would be incredibly useful within GitLab's as well.

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Intended users

Further details

Proposal

Add "View blame prior to this change" functionality to the GitLab UI for navigating previous blames

Permissions and Security

No change to existing blame permissions

Documentation

Testing

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

Using the GitLab UI I can easily traverse the history of a line of code by navigating to previous blames.

What is the type of buyer?

GitLab Starter

Links / references