Add CODEOWNERS

[sptramer]

As part of the actions of accepting o3de/sig-docs-community#61 we need to create a CODEOWNERS file. This should follow the layout as described in the RFC, with the appropriate owners:

• Reviewers/docs-reviewers - A new group created to split from the sig/docs-community reviewer/maintainer pool into different reviewers so that we can enforce the right controls on elements like blogs vs. documentation. Will start with membership identical to sig/docs-community-reviewers with opt-out.
• Reviewers/community-reviewers - The other half of the split. Will start with membership identical to sig/docs-community-reviewers with opt-out.
• Reviewers/web-reviewers - Reviewers for website code and infrastructure changes. This will start with a hand-selected pool of reviewers identified by prior commitments. Other membership will be opt-in.
• Reviewers/*-sig/docs-tech-reviewers - New groups created as subgroups of each existing Reviewers/*-sig subgroup. These are the tech reviewer pools for each individual SIG. This may change based on the outcome of Message acceptance of RFC #61 sig-docs-community#75 if SIGs communicate that they are OK with the tech reviewer and docs reviewer pools being identical.
• lf - The existing pool of Linux Foundation representatives on O3DE.

Tasks

1. Infrastructure setup
2. Create and merge CODEOWNERS

[chanmosq]

Regarding how to populate the group for technical reviewers, RFC o3de/sig-docs-community#74 (and comments) proposes some possible solutions:

1. Using the existing, all-encompassing Reviewers team
2. Further organizing the CODEOWNERS file by assigning SIG reviewer teams to their respective areas in the docs.
3. Populating a separate docs-tech-reviews team

This comment talks about using option 1 to start, and eventually transitioning to option 2.

There's not much strong support for option 3 -- seems like it would be more work that's not necessary, since each SIG is already maintaining their team of reviewers.