init/sync: add --no-tags to match --tags

While this provides a way to undo earlier command line options (e.g.
`repo sync --tags --no-tags`) which can be helpful for scripting &
automation, this more importantly allows the user to override the
manifest settings for syncing tags from a project.

Bug: https://crbug.com/gerrit/12401
Change-Id: Id4c36cd82e6ca7cb073b5d63a09f6c7ccdebba83
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/304904
Reviewed-by: Raman Tenneti <rtenneti@google.com>
Tested-by: Mike Frysinger <vapier@google.com>