Split QA into a dedicated section

Currently, the 'QA package-and-test' section in Danger appears to be
part of the Reviewer Roulette (or the previous Danger section). This
commit splits the QA into a dedicated Danger section.

Related to https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/2839

danger/stable_branch_patch/Dangerfile

@@ -2,7 +2,7 @@
 
 if stable_branch.non_security_stable_branch?
   markdown(<<~MARKDOWN)
-  ### QA `e2e:package-and-test`
+  ## QA `e2e:package-and-test`
 
   **@#{helper.mr_author}, the `package-and-test` job must complete before merging this merge request.***