APPS/cmp: Fix logic and doc of mutually exclusive -server/-use_mock_srv/-port/-rspin...

APPS/cmp: Fix logic and doc of mutually exclusive -server/-use_mock_srv/-port/-rspin options

Ignore -server with -rspin and exclude all of -use_mock_srv/-port/-rspin.
On the other hand, -server is required if no -use_mock_srv/-port/-rspin is given.
Ignore -tls_used with -use_mock_srv and -rspin; it is not supported with -port.
If -server is not given, ignore -proxy, -no_proxy, and -tls_used.
Also slightly improve the documentation of the two mock server variants.

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17254)