Append the current release's changelog body to the git tag message

[frankdugan3]

This will have several benefits, particularly that with GitHub releases, the tag's message will be added into the body.

As @zachdaniel mentioned in a Discord conversation, the implementation should be pretty easy to add:

We'll probably need to update the Changelog.write!/5 function to return the text contents that it wrote to the changelog, and then pass that into the confirm_and_tag function

[zachdaniel]

I won't have much time to focus on this, but I'll try to get around to it in the next couple weeks. If anyone else wants to tackle it I'd be grateful.

[frankdugan3]

I may take a stab at this. Do you think it would be better for Changelog.write/5 to return just the new_content, or perhaps a map/tuple containing both the entire changelog and new_content?

[zachdaniel]

Probably just the new_content since the whole file itself isn't needed for anything further down the line.

[zachdaniel]

This was completed.