Feature request (validation): add OtherReason String in data FailedReason

[lyokha]

This is a feature request. I implemented sending client OCSP requests / parsing OCSP responses after validateDefault in onServerCertificate hook. When an OCSP check fails, the hook returns a single FailedReason. The problem is that there is no appropriate constructor in data FailedReason, and therefore I used CacsheSaysNo "OCSP: ...". Therefore, some OtherReason String constructor would be great for custom validation hooks.