Integrate masking

This uses the masker crate I wrote for this purpose. It does not support the newer gitlab prefixed masking, it just adds all all variable values which are marked as masked to the masker.

We may also want to update the gitlab-runner-rs crate to allow us set the masking feature; I don't think it can be critical because we'll mask both the logs and the output before gitlab ever sees the data, but gitlab might needlessly re-mask the logs.

That likely means that when evaluating this, we need to check the uploaded artifact log for masked data, and not rely on seeing masking in the live log view - that could be from gitlab*