[FEATURE]: RSA X9.31 padding in cryptography registry

[jvdsn]

Describe the feature

Currently the cryptography registry only has families for RSAES-OAEP, RSAES-PKCS1, RSASSA-PKCS1, and RSASSA-PSS. In #841, X9.31 padding was added to the core spec, so it should also be in the cryptography registry.

Additional context

I'm wondering if there should be a generic / catch-all "RSA" family, considering that there is also an "unknown" padding type in the core spec.