fix: avoid cluttering logs with simple message queue polling

[masci]

Fixes #428

After the refactoring, the SimpleMessageQueue behaves like a pubsub system with the client polling for messages, similar to Redis for example. Using plain HTTP calls as the pubsub protocol, the client keeps GETting the endpoint on the server to get messages (if any) for the whole application lifetime, and uvicorn happily fills the access logs with noise.

This PR filters out polling requests to the /messages endpoint from the access logs.

[coveralls]

coverage: 77.68% (+0.04%) from 77.638%
when pulling dfd57cf on massi/simplemessage-logs
into 26b8ad5 on main.