Improve ossl_cmp_msg_check_received() and rename to ossl_cmp_msg_check_update()

Bugfix: allow using extraCerts contained in msg already while checking signature
Improve function name, simplify its return value, and update its documentation

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11998)
