Create CODEOWNERS file

[lbianchi-lbl]

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[MarcusHolly]

A few comments:

1.) Can we add Maojian (Morgan88888888) to the list of WaterTAP members? He's already in the IDAES repo.

2.) Some of us had a discussion offline about how comprehensive the lists should be. Ultimately we landed on including any relevant names. This will help with allocating responsibilities when people are offboarding and also provides some insight into areas of the repo where we could potentially use more support (if there's only 1-2 names listed). It's also just easier to trim down a list of excess names rather than trying to dig for more names. We're open to feedback on this tho.