proxy: random changes (#8602)

## Problem

1. Hard to correlate startup parameters with the endpoint that provided
them.
2. Some configurations are not needed in the `ProxyConfig` struct.

## Summary of changes

Because of some borrow checker fun, I needed to switch to an
interior-mutability implementation of our `RequestMonitoring` context
system. Using https://docs.rs/try-lock/latest/try_lock/ as a cheap lock
for such a use-case (needed to be thread safe).

Removed the lock of each startup message, instead just logging only the
startup params in a successful handshake.

Also removed from values from `ProxyConfig` and kept as arguments.
(needed for local-proxy config)

proxy/src/cache/endpoints.rs

@@ -68,7 +68,7 @@ impl EndpointsCache {
             ready: AtomicBool::new(false),
         }
     }
-    pub async fn is_valid(&self, ctx: &mut RequestMonitoring, endpoint: &EndpointId) -> bool {
+    pub async fn is_valid(&self, ctx: &RequestMonitoring, endpoint: &EndpointId) -> bool {
         if !self.ready.load(Ordering::Acquire) {
             return true;
         }