Github action to review pull requests

[g4s8]

It would be great to provide Aibolit GitHub action to comment on submitted pull requests with warning messages. For example Codecov has similar tool: https://github.com/marketplace/actions/codecov - user enables this Codecov action in GitHub repo, and on each pull request this action performs some kind of review with comments about changed test coverages, like here: https://github.com/artipie/asto/pull/194#issuecomment-638845289

[0crat]

@acheshkov/z please, pay attention to this issue