ci: use docker/metadata-action

[mxinden]

Description

Current approach is not robust to more complex branch names.

Related #4311 (comment).

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[thomaseizinger]

I've changed this to run on master and pull_request instead so we get a tag for the merge commit of a PR, see https://github.com/libp2p/rust-libp2p/pkgs/container/rust-libp2p-server/126912021?tag=pr-4421 for example.

[thomaseizinger]

Weirdly, what seems to have worked in this PR does not work in other PRs: https://github.com/libp2p/rust-libp2p/actions/runs/6156861489/job/16706395686?pr=4275

[mxinden]

@thomaseizinger I am assuming that the failure is due to the fact that it comes from a fork and thus does not have the credentials.

[thomaseizinger]

@thomaseizinger I am assuming that the failure is due to the fact that it comes from a fork and thus does not have the credentials.

Yep, I've fixed that since :)