proxy: connect redis with AWS IAM (#7189)

## Problem

Support of IAM Roles for Service Accounts for authentication.

## Summary of changes

* Obtain aws 15m-long credentials
* Retrieve redis password from credentials
* Update every 1h to keep connection for more than 12h
* For now allow to have different endpoints for pubsub/stream redis.

TODOs: 
* PubSub doesn't support credentials refresh, consider using stream
instead.
* We need an AWS role for proxy to be able to connect to both: S3 and
elasticache.

Credentials obtaining and connection refresh was tested on xenon
preview.

https://github.com/neondatabase/cloud/issues/10365

proxy/src/serverless/websocket.rs

@@ -1,5 +1,5 @@
 use crate::{
-    cancellation::CancellationHandler,
+    cancellation::CancellationHandlerMain,
     config::ProxyConfig,
     context::RequestMonitoring,
     error::{io_error, ReportableError},
@@ -134,7 +134,7 @@ pub async fn serve_websocket(
     config: &'static ProxyConfig,
     mut ctx: RequestMonitoring,
     websocket: HyperWebsocket,
-    cancellation_handler: Arc<CancellationHandler>,
+    cancellation_handler: Arc<CancellationHandlerMain>,
     hostname: Option<String>,
     endpoint_rate_limiter: Arc<EndpointRateLimiter>,
 ) -> anyhow::Result<()> {