Allow push-to-pull-request-branch to optionally update the pull request title (and body?)

[dsyme]

In practice adding new commits to a PR often means the title should be logically updated. Some people will also want the body to be updated.

We should allow these as separate options on push-to-pull-request-branch.

[pelikhan]

There is a dedicated safe output for this already. We should avoid overlapping.

[pelikhan]

Update of pull request description is involved (append vs replace vs replace-island). It will bloat this adage output.

[pelikhan]

Reopen as needed.

Use update-pull-request.