Add OSSL_CMP_CTX_get0_validatedSrvCert(), correcting OSSL_CMP_validate_msg()

Add OSSL_CMP_CTX_get0_validatedSrvCert(), correcting OSSL_CMP_validate_msg()

Also change ossl_cmp_ctx_set0_validatedSrvCert() to ossl_cmp_ctx_set1_validatedSrvCert(),
and add respective tests as well as the -srvcertout CLI option using the new function.

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
(Merged from https://github.com/openssl/openssl/pull/18656)