Enforce RTC (#320)

This is an implementation of the [PMC vote in `dev@logging`](https://lists.apache.org/thread/8ffdw1zqrvwrsdr0ng0m2rgtdnpzg4hk).
I didn't add any required checks, since:

- Any test can fail because of a problem in `logging-log4j2`, not this repo.
- I don't really know which checks should be added.

Author: ppkarwasz

.asf.yaml

@@ -47,4 +47,10 @@ github:
   # Prevent force pushes to primary branches
   protected_branches:
     main:
+      # All commits must be signed
       required_signatures: true
+      # All reviews must be addressed before merging
+      required_conversation_resolution: true
+      # At least one positive review must be present
+      required_pull_request_reviews:
+        required_approving_review_count: 1