MEDIUM: ssl: Add ocsp_certid in ckch structure and discard ocsp buffer early

MEDIUM: ssl: Add ocsp_certid in ckch structure and discard ocsp buffer early

The ocsp_response member of the cert_key_and_chain structure is only
used temporarily. During a standard init process where an ocsp response
is provided, this ocsp file is first copied into the ocsp_response
buffer without any ocsp-related parsing (see
ssl_sock_load_ocsp_response_from_file), and then the contents are
actually interpreted and inserted into the actual ocsp tree
(cert_ocsp_tree) later in the process (see ssl_sock_load_ocsp). If the
response was deemed valid, it is then copied into the actual
ocsp_response structure's 'response' field (see
ssl_sock_load_ocsp_response). From this point, the ocsp_response field
of the cert_key_and_chain object could be discarded since actual ocsp
operations will be based of the certificate_ocsp object.

The only remaining runtime use of the ckch's ocsp_response field was in
the CLI, and more precisely in the 'show ssl cert' mechanism.
This constraint could be removed by adding an OCSP_CERTID directly in
the ckch because the buffer was only used to get this id.

This patch then adds the OCSP_CERTID pointer in the ckch, it clears the
ocsp_response buffer early and simplifies the ckch_store_build_certid
function.