Aggregate results from all jobs into a singular GitHub comment

[jkaczman]

It would be cool if there was a way to aggregate the results from all jobs run on a singular PR into a singular comment.

• Here's an example of 3 separate comments on a single PR: ci: check to make sure bencher works with fire-and-forget pgdogdev/pgdog#1677

I believe this is the way it is because we run 3 different jobs to try to get parallelism. If we didn't use --ci-id, the separate jobs right now would overwrite each other instead of showing a table of 3.

This isn't a blocker for us (we only comment on regression), but it would be great for aesthetics if parallelism is encouraged in the future