MINOR: ssl: Add sample fetches related to OCSP update

MINOR: ssl: Add sample fetches related to OCSP update

This patch adds a series of sample fetches that rely on the specified
OCSP update context structure. They will then be of use only in the
context of an ongoing OCSP update.
They cannot be used directly in the configuration so they won't be made
public. They will be used in the OCSP update's specific log format which
should be emitted by the update task itself in a future patch.