Adds docker compose examples (#1113)

This adds three example docker-compose files:

- A basic Grist instance backed by sqlite, with no additional services.
- A Grist instance that uses Postgres, Redis and MinIO.
- A Grist instance that uses OIDC authentication and traefik.

These are intended to be customised by self-hosters for their own needs.

All examples should work without any additional configuration.

docker-compose-examples/grist-local-testing/README.md

@@ -0,0 +1,12 @@
+This is the simplest example that runs Grist, suitable for local testing.
+
+It is STRONGLY RECOMMENDED not to use this container in a way that makes it accessible to the internet.
+This setup lacks basic security or authentication.
+
+Other examples demonstrate how to set up authentication and HTTPS.
+
+See https://support.getgrist.com/self-managed for more information.
+
+## How to run this example
+
+This example can be run with `docker compose up`.

docker-compose-examples/grist-local-testing/docker-compose.yml

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+services:
+  grist:
+    image: gristlabs/grist:latest
+    volumes:
+      # Where to store persistent data, such as documents.
+      - ${PERSIST_DIR}/grist:/persist
+    ports:
+      - 8484:8484