container image advisories show extra flags

[yazug]

When you have a container image advisory, it can only have container images in it.

The following flags I've noticed show up but are meaningless

• tps
• distqa
• sigs
• need_sigs

The following might be good to add if not already supported:

• push to staging

[ktdreyer]

There is a push() method (added in #88) but nothing documented for this yet

[ktdreyer]

push() is now documented, and I've tested that it works for container advisories.

[phracek]

push() method works as well from my point of view.