feat: allow logging the SQL query to stderr

- Logs the main SQL query when `log-query=main-query`.
- Only logs at the current `log-level`.

test/io/configs/no-defaults-env.yaml

@@ -28,6 +28,7 @@ PGRST_JWT_SECRET: c2VjdXJpdHl0aHJvdWdob2JzY3VyaXR5aW5iYXNlNjQ=
 PGRST_JWT_SECRET_IS_BASE64: true
 PGRST_JWT_CACHE_MAX_LIFETIME: 86400
 PGRST_LOG_LEVEL: info
+PGRST_LOG_QUERY: 'main-query'
 PGRST_OPENAPI_MODE: 'ignore-privileges'
 PGRST_OPENAPI_SECURITY_ACTIVE: true
 PGRST_OPENAPI_SERVER_PROXY_URI: 'https://postgrest.org'