feat(prometheus): add wasmx metrics

[casimiro]

Summary

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #[issue number]

[flrgh]

Thanks for all the work you've put into this!

I left a couple inline comments about small things to address before merge, but it's looking good to me.

[samugi]

thanks for addressing the feedback and providing additional details, looks good to me

[flrgh]

rebasing...

[team-gateway-bot]

Cherry-pick failed for master, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally.

git remote add upstream https://github.com/kong/kong-ee
git fetch upstream master
git worktree add -d .worktree/cherry-pick-13681-to-master-to-upstream upstream/master
cd .worktree/cherry-pick-13681-to-master-to-upstream
git checkout -b cherry-pick-13681-to-master-to-upstream
ancref=$(git merge-base dcf89f39e85bd91fb7a3798c5a36b5d6f384a264 09e0704dc4964f46cf5f00cb66cff5dc27b82f6f)
git cherry-pick -x $ancref..09e0704dc4964f46cf5f00cb66cff5dc27b82f6f