Always prompt user to amend if rebase is in progress

[james-seymour-cubiko]

I accidentally used gs commit amend today when I was done finishing a rebase conflict instead of gs rebase continue which was a bit of a headache to fix!

I see that this is already somewhat handed in that if there is at least one unmerged path the user will be prompted to continue with amending, but I accidentally ran this after fixing all merge conflicts first so didn't get this prompt - appreciate that this is an edge case, but I think it could be useful to still prompt the user to continue with the amend even if all rebase conflicts are resolved?

If not, I should be able to just remember not to gs commit amend next time!

[abhinav]

I've made this mistake in the past too, so I think a prompt makes sense.
But not for all rebase states.
I frequently use edit or break rebase instructions to edit existing commits,
and prompting in those cases would be burden.
If we can find a way to determine that the commit we're about to make is a rebase resolution, we can prompt in that case.

I'll try to poke around information available from Git and inside .git to see
if there's an obvious way to know we're resolving a conflict.
Alternatively, we might be able to make git-spice remember that it encountered a conflict (and not a deliberate interruption)
and use that to decide whether commit amend should prompt.