issues/copy: specify target repo based on mapping

[Skaty]

Current Behaviour

When the copy function is executed, the issues are copied to a single target repository. There is currently no support for multiple repositories.

New Behaviour

The copy function will be able to:

• [x] Copy issues to different organisations (subject to permissions)
• [x] Vary the destination repository based on the image of the mapping.

New Command Structure

• torepo argument - modify to take in a repository name in org/repo format. Additionally, the argument may be expressed as a Python 3 format string (e.g. org{}/repo). The replacement field will be replaced with the mapping's output.

[damithc]

@Skaty we still need the old behavior for final testing. This one is an additional functionality to be used for mock testing in week 11.

[Skaty]

@damithc As stated above, the torepo format "may" be expressed as a Python 3 format string. As such, the format string is entirely optional and if omitted, would result in the old behaviour.