Add CODEOWNERS file

[raulchen]

What do these changes do?

Add the CODEWONERS file, which defines the owners of each module. When a PR touches a file of a module, the corresponding owners will be automatically added as reviewers.

Related issue number

Linter

• I've run scripts/format.sh to lint the changes in this PR.

[raulchen]

The owners are grouped by teams, e.g. @ray-project/ray-core-cpp. I haven't created those teams yet. Please let me know if you have better ideas about how to categorize the code.

[ericl]

I would exclude ci/ since a lot of RLlib / tune / misc tests go through this.

[raulchen]

Changed this to only include the CI scripts.

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[robertnishihara]

It might make sense to make it even more fine-grained, e.g., also include the autoscaler and the build system as two separate groups. We can also try what you have and see if it's helping and iterate.

[raulchen]

yeah, we can try this first and make it more fine-grained later.
Comments are addressed.

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[raulchen]

@robertnishihara @ericl any other comments?

[ericl]

Looks good, let's try it out