Document docker and helm tags better

[pmeier]

We currently only explain how releases are done

https://github.com/nebari-dev/nebari-chat-pack/blob/a456c7567f978f5560d4865b7e85d535b77549f1/README.md?plain=1#L50-L55

but we never explain what tags / versions are available. Common tags are defined in

https://github.com/nebari-dev/nebari-chat-pack/blob/a456c7567f978f5560d4865b7e85d535b77549f1/.github/actions/workflow-metadata/action.yml#L108-L115

For docker there are some additional tags in

https://github.com/nebari-dev/nebari-chat-pack/blob/a456c7567f978f5560d4865b7e85d535b77549f1/.github/workflows/docker.yml#L60-L62

We need two types of documentation:

1. Static inside the README for releases and pushes to main
2. Dynamic as comments on PRs to always show the docker and helm tags of the latest built commit. Docker and helm tags should have independent comments that get updated after every build. We can use something like https://github.com/mshick/add-pr-comment (feel free to pick something else; this is just the first thing I found without validating it more)