Auto-run gh auth setup-git on profile switch

[jhmaster2000]

The issue cli/cli#6096 severely reduces the usefulness of gh-profile since the profile switch command doesn't update the user.{name,email} fields. The linked issue already has a PR waiting to merge: cli/cli#6643.

Once that is merged gh-profile should be fixable with little effort by simply adding the following steps to profile switch:

1. After the switch, run git config --unset user.name and git config --unset user.email *
2. Run gh auth setup-git

* According to cli/cli#6096 (comment), it may be implemented in such a way that it won't set the values if they're already set, hence unsetting them first may be necessary.