Add codeowners

[marcodamore]

As per our thread in #wg-dbt-core-semantic-layer, we've decided to require more code reviewers from Metricflow, core, and product owners to make sure the specs we merge to dsi are well reviewed

Resolves #

Description

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• This PR includes tests, or tests are not required/relevant for this PR
• I have run changie new to create a changelog entry

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Marco d'Amore.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email [email protected]
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[QMalcolm]

I added the Skip Changelog label to skip the changelog step.