[git propose] Allow passing a --title and --body

[ruudk]

I'd like to be able to pass a title and body when proposing a change (creating a pull request).

GitHub supports this, by sending the following query parameters: ?expand=1&title=title&body=body.

I'd like to use this in my custom script that automatically finds a title (using AI) and a body (by taking all commit messages).

It would be great if the body can also be passed via stdin like gh cli does:

echo "long\nbody" | gh pr create --web --title "$TITLE" --body-file -

[ruudk]

When you create a PR on GitHub and there is only 1 commit, GitHub will use the commit title as the title of the PR.

Maybe Git Town can do the same. If there is only 1 commit, then use that as a title. If there are more than 1 commit, ask for a custom title.