Add simplified helm chart (#2905)

As discussed yesterday, a simplified version of [my
helm](https://github.com/S7evinK/dendrite-helm) which deploys a monolith
with internal NATS and an optionally enabled PostgreSQL server. If the
PostgreSQL dependency is not enabled, a user specified connection string
is constructed.

Co-authored-by: kegsay <kegan@matrix.org>

.github/workflows/k8s.yml

@@ -0,0 +1,90 @@
+name: k8s
+
+on:
+  push:
+    branches: ["main"]
+    paths:
+      - 'helm/**' # only execute if we have helm chart changes
+  pull_request:
+    branches: ["main"]
+    paths:
+      - 'helm/**'
+
+jobs:
+  lint:
+    name: Lint Helm chart
+    runs-on: ubuntu-latest
+    outputs:
+      changed: ${{ steps.list-changed.outputs.changed }}
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+      - uses: azure/setup-helm@v3
+        with:
+          version: v3.10.0
+      - uses: actions/setup-python@v4
+        with:
+          python-version: 3.11
+          check-latest: true
+      - uses: helm/chart-testing-action@v2.3.1
+      - name: Get changed status
+        id: list-changed
+        run: |
+          changed=$(ct list-changed --config helm/ct.yaml --target-branch ${{ github.event.repository.default_branch }})
+          if [[ -n "$changed" ]]; then
+              echo "::set-output name=changed::true"
+          fi
+
+      - name: Run lint
+        run: ct lint --config helm/ct.yaml
+
+  # only bother to run if lint step reports a change to the helm chart
+  install:
+    needs:
+      - lint
+    if: ${{ needs.lint.outputs.changed == 'true' }}
+    name: Install Helm charts
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+          ref: ${{ inputs.checkoutCommit }}
+      - name: Install Kubernetes tools
+        uses: yokawasa/action-setup-kube-tools@v0.8.2
+        with:
+          setup-tools: |
+            helmv3
+          helm: "3.10.3"
+      - uses: actions/setup-python@v4
+        with:
+          python-version: "3.10"
+      - name: Set up chart-testing
+        uses: helm/chart-testing-action@v2.3.1
+      - name: Create k3d cluster
+        uses: nolar/setup-k3d-k3s@v1
+        with:
+          version: v1.21
+      - name: Remove node taints
+        run: |
+          kubectl taint --all=true nodes node.cloudprovider.kubernetes.io/uninitialized- || true
+      - name: Run chart-testing (install)
+        run: ct install --config helm/ct.yaml
+
+      # Install the chart using helm directly and test with create-account
+      - name: Install chart
+        run: |
+          helm install --values helm/dendrite/ci/ct-postgres-sharedsecret-values.yaml dendrite helm/dendrite
+      - name: Wait for Postgres and Dendrite to be up
+        run: |
+          kubectl wait --for=condition=ready --timeout=90s pod -l app.kubernetes.io/name=postgresql || kubectl get pods -A
+          kubectl wait --for=condition=ready --timeout=90s pod -l app.kubernetes.io/name=dendrite || kubectl get pods -A
+          kubectl get pods -A
+          kubectl get services
+          kubectl get ingress
+      - name: Run create account
+        run: |
+          podName=$(kubectl get pods -l app.kubernetes.io/name=dendrite -o name)
+          kubectl exec "${podName}" -- /usr/bin/create-account -username alice -password somerandompassword