- add parameter to `conn_is_alive()` cfilter method that returns
if there is input data waiting on the connection
- refrain from re-using connnection from the cache that have
input pending
- adapt http/2 and http/3 alive checks to digest pending input
to check the connection state
- remove check_cxn method from openssl as that was just doing
what the socket filter now does.
- add tests for connection reuse with special server configs
Closes#10690
