ci: added auto assign reviews

[infvg]

No description provided.

[philo-he]

@infvg, Thanks for the proposal.

If I understand correctly, this PR implements a round-robin assignment. My concern is that Gluten has several fairly independent scopes — Velox backend, ClickHouse backend, Flink, Iceberg, Delta, etc. — and reviewing each effectively depends a lot on the reviewer's expertise in that area. A purely round-robin assignment may route a PR to someone outside the relevant scope.

For the review process, I'd suggest something like:

First, give a short buffer (say ~1 day) for reviewers familiar with the related scope to notice the PR and pick it up.
If it's still pending after ~2 days with no reviewer, have someone who knows the community well (e.g. @zhouyuan, or others) assign it to the one or more appropriate reviewers.

I also think we should encourage broader participation in reviews — including non-committers, who are very welcome to review. Separately, it seems review turnaround has been slower than before. If that's the case, it might be worth raising it with the community so we can encourage more active reviewing.

[infvg]

@philo-he
IMO the goal isn’t to make assigned reviewers the only reviewers, it’s mainly to make sure PRs get an initial look and encourage more people to participate. Anyone else can still review, and then committers can do a final pass before they merge. For example, Presto has a bot that adds 1-2 people to every PR just for an initial pass. Those people generally aren't the ones who merge/approve (and sometimes they don't even review), but it encourages more participation.

I changed it to use reviewer groups per area, for example like an Iceberg group, Clickhouse group or a global group, instead of one global round-robin. Anyone interested in an area could add themselves to that group. That should help keep reviews closer to the right person while also helping people stay involved with whichever part of the codebase they want.