Add weekly GitHub Actions workflow to maintain an up to date reviewer list

[damccorm]

This will:

 

• Get all closed PRs from the last 3 months
• For each set of reviewers for an area, look at all PRs in that area and find all contributors who have authored or reviewed at least 5 PRs (this value can be tuned over time).
• Create a PR to update our reviewer list to include those reviewers and exclude any existing reviewers who don't meet that criteria. All new reviewers will need to approve before the PR is merged. Any suggested reviewers who would not like to be suggested again can add themselves to the exclusionList.

 

More info here - https://docs.google.com/document/d/1FhRPRD6VXkYlLAPhNfZB7y2Yese2FCWBzjx67d3TjBo/edit#heading=h.ncgdizak1sfo

Imported from Jira BEAM-13929. Original Jira may contain additional context.
Reported by: damccorm.
Subtask of issue #21417