TUN-8621: Prevent QUIC connection from closing before grace period after unregistering

Whenever cloudflared receives a SIGTERM or SIGINT it goes into graceful shutdown mode, which unregisters the connection and closes the control stream. Unregistering makes it so we no longer receive any new requests and makes the edge close the connection, allowing in-flight requests to finish (within a 3 minute period).
 This was working fine for http2 connections, but the quic proxy was cancelling the context as soon as the controls stream ended, forcing the process to stop immediately.

 This commit changes the behavior so that we wait the full grace period before cancelling the request

CHANGES.md

@@ -1,3 +1,7 @@
+## 2024.9.2
+### Bug Fixes
+- We fixed a bug related to `--grace-period`. Tunnels that use QUIC as transport weren't abiding by this waiting period before forcefully closing the connections to the edge. From now on, both QUIC and HTTP2 tunnels will wait for either the grace period to end (defaults to 30 seconds) or until the last in-flight request is handled. Users that wish to maintain the previous behavior should set `--grace-period` to 0 if `--protocol` is set to `quic`. This will force `cloudflared` to shutdown as soon as either SIGTERM or SIGINT is received.
+
 ## 2024.2.1
 ### Notices
 - Starting from this version, tunnel diagnostics will be enabled by default. This will allow the engineering team to remotely get diagnostics from cloudflared during debug activities. Users still have the capability to opt-out of this feature by defining `--management-diagnostics=false` (or env `TUNNEL_MANAGEMENT_DIAGNOSTICS`).