ci: run functional test 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 against it;
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
functional suite. Actions are pinned to commit SHAs per repo convention.

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

Author: TerryHowe

.github/workflows/functional.yml

@@ -0,0 +1,62 @@
+# Copyright The ORAS Authors.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: functional
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - '**/*.go'
+      - 'go.mod'
+      - 'go.sum'
+      - 'test/functional/**'
+      - '.github/workflows/functional.yml'
+  pull_request:
+    branches:
+      - main
+    paths:
+      - '**/*.go'
+      - 'go.mod'
+      - 'go.sum'
+      - 'test/functional/**'
+      - '.github/workflows/functional.yml'
+
+permissions:
+  contents: read
+
+concurrency:
+  group: functional-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  functional:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Set up Go environment
+        uses: actions/setup-go@b7ad1dad31e06c5925ef5d2fc7ad053ef454303e # v7.0.0
+        with:
+          go-version: '1.25'
+          check-latest: true
+      - name: Create kind cluster
+        # Writes a kubeconfig to the default path (~/.kube/config), which the
+        # suite's buildKubeConfig() reads. TestMain deploys zot into the
+        # cluster from test/functional/testdata/k8s.
+        uses: helm/kind-action@a1b0e391336a6ee6713a0583f8c6240d70863de3 # v1.12.0
+      - name: Run functional tests
+        working-directory: test/functional
+        run: go test -v -timeout 25m ./...