CMP docs: clarify behavior on message/total timeout values given

CMP docs: clarify behavior on message/total timeout values given

Clarify behavior of OSSL_CMP_CTX_set_option() when given (negative)
values for OSSL_CMP_OPT_MSG_TIMEOUT or OSSL_CMP_OPT_TOTAL_TIMEOUT.
Fix doc of -msg_timeout and -total_timeout in openssl-cmp.pod.in

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
(Merged from https://github.com/openssl/openssl/pull/19391)