proxy: Relax endpoint check (#6503)

## Problem

http-over-sql allowes host to be in format api.aws.... however it's not
the case for the websocket flow.

## Summary of changes

Relax endpoint check for the ws serverless connections.

proxy/src/serverless.rs

@@ -41,6 +41,8 @@ use tokio_util::sync::CancellationToken;
 use tracing::{error, info, info_span, warn, Instrument};
 use utils::http::{error::ApiError, json::json_response};
 
+pub const SERVERLESS_DRIVER_SNI: &str = "api";
+
 pub async fn task_main(
     config: &'static ProxyConfig,
     ws_listener: TcpListener,