When creating a TCP proxy bridge for Connect tasks, we are at the
mercy of either end for managing the connection state. For long
lived gRPC connections the proxy could reasonably expect to stay
open until the context was cancelled. For the HTTP connections used
by connect native tasks, we experience connection disconnects.
The proxy gets recreated as needed on follow up requests, however
we also emit a WARN log when the connection is broken. This PR
lowers the WARN to a TRACE, because these disconnects are to be
expected.

Ideally we would be able to proxy at the HTTP layer, however Consul
or the connect native task could be configured to expect mTLS, preventing
Nomad from MiTM the requests.

We also can't mange the proxy lifecycle more intelligently, because
we have no control over the HTTP client or server and how they wish
to manage connection state.

What we have now works, it's just noisy.

Fixes #10933