ci: run k8sfunctional suite on a kind cluster

Adds .github/workflows/functional.yml. The job provisions an ephemeral
Kubernetes cluster with kind and runs the test/functional module with the
k8sfunctional build tag; TestMain deploys zot from testdata/k8s and the tests
exercise the public API end-to-end. Runs on pushes and PRs to main that touch
Go sources or the suite. Actions are pinned to commit SHAs per repo convention.

Signed-off-by: Terry Howe <terrylhowe@gmail.com>

Author: TerryHowe

.github/workflows/functional.yml

@@ -59,4 +59,6 @@ jobs:
         uses: helm/kind-action@a1b0e391336a6ee6713a0583f8c6240d70863de3 # v1.12.0
       - name: Run functional tests
         working-directory: test/functional
-        run: go test -v -timeout 25m ./...
+        # The suite is behind the k8sfunctional build tag; without it go test
+        # compiles and runs nothing.
+        run: go test -tags k8sfunctional -v -timeout 25m ./...