Duplicate issues

[sajidanower23]

If issue # x is already present in dest repo, it should not be created again.
Solving this requires some thought.

• We could disregard doing anything for every # x that also exists in dest, but that would mean that if there is a difference between source issue #x and dest # x, that difference gets lost.
• We could overwrite dest # x with source # x, but then the difference, again, gets lost

That being said, I think it is a reasonable expectation that the destination repo is empty, and therefore we could overwrite the contents of every # x in dest repo