Add AlreadyRevoked handling to revokedCertificates table inserts

[aarongable]

Within sa.addRevokedCertificate, detect if the insert failed due to a duplicate primary key, and return berrors.AlreadyRevoked in that case. This matches the behavior of sa.RevokeCertificate when an update to the certificateStatus table modifies no rows.

This change has no immediate impact, because addRevokedCertificate is only called after RevokeCertificate's update to the certificateStatus table has succeeded: if the first operation returns AlreadyRevoked, this code is never reached. However, we plan to remove the certificateStatus table in the future, so this code will need to return AlreadyRevoked when appropriate.

Part of #8322

---

Warning

Do not merge before #8427
Do not merge before IN-11835 is complete