Update the CODEOWNERS to capture the current reviewers and contributors

[rtyler]

We have a few folks who were once very active but no longer spend much time with us 🤗

I believe we should remove the following from the * rule in CODEOWNERS to make our reviews cleaner and to spare their inboxes and notifications:

• @mosyp
• @houqp
• @xianwill

I think once #1434 is completed, we can and should add some more folks as CODEOWNERS with more granularity 🥳