Add command for transferring repositories

[x3ro]

Describe the feature or problem you'd like to solve

Transferring repositories to a new namespace is cumbersome using the Gitlab UI, especially when it's not just a single one. As a result, it'd be nice if glab had the ability to automate this.

Propose a Solution

I've got a working prototype implemented in this branch. The contribution guidelines state I should add an issue before opening a PR, so here I am :)

Additional context

Since transferring a repositories is an operation that cannot be undone, I've added a long warning message as well as a confirmation prompt (see below, typo is already fixed). Feedback is welcome:

[zemzale]

This is a nice feature indeed @x3ro.

I looked at the branch and it looks pretty good. I might have to play with it a bit to see how it all works, but for the first iteration of the feature, this would be nice.

Feel free to open the PR and if there are some comments about we can talk about that there.

[clemsbot]

This issue has been automatically marked as stale because it has not had recent activity. We haven't had the time to address it yet, but we want to keep it open. This message is just a reminder for us to help triage issues.