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>

llama_stack/core/entrypoint.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+set -euo pipefail
+
+determine_server_command() {
+    local server_args=()
+
+    # The env variable will take precedence over the config file
+    if [ -n "${ENABLE_POSTGRES_STORE:-}" ]; then
+        server_args=("python3" "-m" "llama_stack.core.server.server" "starter::run-with-postgres-store")
+    elif [ -n "$1" ]; then
+        server_args=("python3" "-m" "llama_stack.core.server.server" "$1")
+    fi
+    echo "${server_args[@]}"
+}
+
+main() {
+    echo "Starting Llama Stack server..."
+
+    local server_command
+    server_command=$(determine_server_command "$@")
+
+    if [[ -z "$server_command" ]]; then
+        echo "Error: Could not determine server command"
+        exit 1
+    fi
+
+    printf "Executing: %s\n" "$server_command"
+    exec $server_command
+}
+
+main "$@"