feat: ability to use postgres as store for starter distro

The starter distribution now comes with all the required packages to
support persistent stores—like the agent store, metadata, and
inference—using PostgreSQL.  We’ve added a new run YAML file,
run-with-postgres-store.yaml, to make this setup easy. The file is
included in the container image, so users can simply override the
entrypoint to use the Postgres-specific config.  The documentation has
been updated with instructions on how to do that.

Closes: #2619
Signed-off-by: Sébastien Han <seb@redhat.com>

docs/source/distributions/self_hosted_distro/starter.md

@@ -186,6 +186,35 @@ docker run \
   --port $LLAMA_STACK_PORT
 ```
 
+To run the distribution with a Postgres store, you can use the following command to override the entrypoint:
+
+```bash
+docker run \
+  -it \
+  --pull always \
+  -p $LLAMA_STACK_PORT:$LLAMA_STACK_PORT \
+  -e OPENAI_API_KEY=your_openai_key \
+  -e FIREWORKS_API_KEY=your_fireworks_key \
+  -e TOGETHER_API_KEY=your_together_key \
+  -e POSTGRES_HOST=your_postgres_host \
+  -e POSTGRES_PORT=your_postgres_port \
+  -e POSTGRES_DB=your_postgres_db \
+  -e POSTGRES_USER=your_postgres_user \
+  -e POSTGRES_PASSWORD=your_postgres_password \
+  --entrypoint python \
+  llamastack/distribution-starter \
+  -m llama_stack.distribution.server.server \
+  --config run-with-postgres-store.yaml
+```
+
+Postgres environment variables:
+
+- `POSTGRES_HOST`: Postgres host (default: `localhost`)
+- `POSTGRES_PORT`: Postgres port (default: `5432`)
+- `POSTGRES_DB`: Postgres database name (default: `llamastack`)
+- `POSTGRES_USER`: Postgres username (default: `llamastack`)
+- `POSTGRES_PASSWORD`: Postgres password (default: `llamastack`)
+
 ### Via Conda or venv
 
 Ensure you have configured the starter distribution using the environment variables explained above.