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/helm.yml

@@ -0,0 +1,39 @@
+name: Release Charts
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - 'helm/**' # only execute if we have helm chart changes
+
+jobs:
+  release:
+    # depending on default permission settings for your org (contents being read-only or read-write for workloads), you will have to add permissions
+    # see: https://docs.github.com/en/actions/security-guides/automatic-token-authentication#modifying-the-permissions-for-the-github_token
+    permissions:
+      contents: write
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+
+      - name: Configure Git
+        run: |
+          git config user.name "$GITHUB_ACTOR"
+          git config user.email "$GITHUB_ACTOR@users.noreply.github.com"
+
+      - name: Install Helm
+        uses: azure/setup-helm@v3
+        with:
+          version: v3.10.0
+
+      - name: Run chart-releaser
+        uses: helm/chart-releaser-action@v1.4.1
+        env:
+          CR_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
+        with:
+          config: helm/cr.yaml
+          charts_dir: helm/