Stop using a deprecated function when creating a certificate in tacd

[breard-r]

The function acme_common::crypto::openssl_certificate::gen_certificate() uses X509Extension::new which is deprecated by the openssl crate since version 0.10.51.

Currently, the extensions module does not provide the structure for the acmeIdentifier extension introduced by RFC 8737, leaving no other choice than using X509Extension::new_from_der.

The use of deprecated function warning has been silenced, however it is not a long-term solution. The call to X509Extension::new should be replaced by something else.