Code owners for new component (exporter/prometheus)

[evan361425]

I recently try to add a new component (exporter/prometheus) in #6975, but no idea who to tag for reviewing.

Do this project planning to add some CODE_OWNER file which helps me tag some users to kindly notify them?

[atoulme]

Our team reviews all PRs. There is no need to assign them. Thank you for your contribution.