chore(22.04): add pkg-deps job (canonical#188)

This commit adds a new pkg-deps job on Pull Request. It checks in
changed files if slices of any package A has been listed in "essential"
of a slice in package B, but B does not depend on A. If found, the CI
will add a comment in the Pull Request with the findings.

.github/workflows/ci.yaml

@@ -19,3 +19,8 @@ jobs:
   lint:
     name: Lint
     uses: canonical/chisel-releases/.github/workflows/lint.yaml@main
+
+  pkg-deps:
+    if: github.event_name == 'pull_request'
+    name: Package dependencies
+    uses: canonical/chisel-releases/.github/workflows/pkg-deps.yaml@main