[WIP] Delete and recreate existing tag

[movermeyer]

What are you trying to accomplish?

Fixes #149
Fixes #171
Resolves 2934fce#r58642151

Both of these are a result of the tag associated with the release not updating to match the new target_commitish.

What approach did you choose and why?

I added a boolean move_existing_tag flag that explicitly requests the deletion of the existing tag of an existing release.

This is opt-in, explicit behaviour, since most tags are considered to be immutable. However, some projects may decide that

What should reviewers focus on?

Assume that I have no idea what's going on.

I tried to research whether there was any problem with deleting lightweight tags, and everything I've found says that doing this is OK...

• Tags are not part of the git log, so you don't have to rewrite history to delete them.

Deleting a lightweight tag is not such a big deal, but deleting an annotated tag, which is a bona fide Git object, should count as deleting local history.
-https://stackoverflow.com/a/25722673

WIP Status

• Actually test it
  • Automated unit tests
  • Manual testing
• We probably need to actually resolve the target_committish values to their SHAs and compare those?

The impact of these changes

Users will be able to opt into having update the commit that a tag points at as part of the release update.

Testing

Totally untested. WIP...