Enable automation of PR review assignments across repos

[clyne]

Investigate and hopefully enable GitHub's "round robin" reviewer assignment for all repos as described here:

https://docs.github.com/en/organizations/organizing-members-into-teams/managing-code-review-assignment-for-your-team#routing-algorithms

[clyne]

Need guidance from @kmpaul on how this working. @andersy005 believes the RR algo is tied to the teams: @ProjectPythia/education and @ProjectPythia/infrastructure. I.e. if one of these teams is tagged, automated RR scheduling will be used. The process is NOT completely automated. The PR submitter has to select one of the teams before scheduling kicks off. Could we further automate? I.e. if tagged infrastructure the "infrastructure" team is selected.

N.B. configuration is here: https://github.com/orgs/ProjectPythia/teams/infrastructure/edit/review_assignment

and https://github.com/orgs/ProjectPythia/teams/education/edit/review_assignment

[dopplershift]

I think we can get this completely automated by adding a team to CODEOWNERS.