Make proxy shutdown when all connections are closed (#3764)

## Describe your changes
Makes Proxy start draining connections on SIGTERM.
## Issue ticket number and link
#3333

proxy/src/http/websocket.rs

@@ -22,6 +22,7 @@ use tokio::{
     io::{self, AsyncBufRead, AsyncRead, AsyncWrite, ReadBuf},
     net::TcpListener,
 };
+use tokio_util::sync::CancellationToken;
 use tracing::{error, info, info_span, warn, Instrument};
 use utils::http::{error::ApiError, json::json_response};
 
@@ -188,6 +189,7 @@ async fn ws_handler(
 pub async fn task_main(
     config: &'static ProxyConfig,
     ws_listener: TcpListener,
+    cancellation_token: CancellationToken,
 ) -> anyhow::Result<()> {
     scopeguard::defer! {
         info!("websocket server has shut down");
@@ -231,6 +233,7 @@ pub async fn task_main(
 
     hyper::Server::builder(accept::from_stream(tls_listener))
         .serve(make_svc)
+        .with_graceful_shutdown(cancellation_token.cancelled())
         .await?;
 
     Ok(())