gitlab: support passing --rev to the `update-all` script

While it's already possible to invoke `update-data` with the `--rev`
argument, one still needs to run all later phases manually.

Fix this, by having `update-all` also accept a `--rev` argument, and
pass it down to `update-data`.

Also, make the help text a bit more usable, by suggesting the usual
versioning scheme used these times.