Consider logging the SPKI hash at issuance time for easier log searches

The SPKI hash is what we use to identify compromised keys: it's one of the more common input methods to the admin block-key tool, and it's what we store in the blockedKeys table. But it's good to get a sense of what certs will be affected before blocking a key, querying the keyHashToSerial table can be slow, and running queries directly against the database is generally a bad practice.

So what if we could do that same query via logs in our log query system instead? If we include the SPKI hash in our issuance logs it'll be very easy for our log search to quickly identify all affected certificates in the last 90 days.