Introduce checks for dependent PRs

[gastaldi]

When a large PR is split into smaller chain of dependent PRs or if it is common for you to have a single change that spans several other pull requests spread out across multiple projects, and if the order in which they are merged is significant, it would be nice if Quarkus bot checked that to prevent accidental merges

See: https://github.com/marketplace/dpulls

[gsmet]

Is it really a problem in practice? I can recall a few cases but it doesn't happen that often IMO.

Anyway, it could be a good first issue.