Make "git tag" create both simple and signed tags

Make "git tag" create both simple and signed tags

A simple tag is just a direct pointer to the object, while a signed tag
is a pointer to a "tag object" that has a pgp signature and points to
the object we tagged.

Use "git tag -s tagname" to create a signed tag.

The "-f" flag overwrites any previous tag of that name (useful if you
update a tag to point to a newer version for things like "latest" etc
tags that aren't necessarily static versions).