Re-evaluate cryptography library usage

[ssciolla]

@lsloan and @jonespm, I'd like some feedback here. I asked @lsloan to remove jwtcrypto in #1101, and I think he took the initiative to see if he could also remove pycryptodome -- which worked at the time I guess? However, when I removed pyOpenSSL, it seems to have broken the createkeys management command (and maybe also getjwk). Adding pycryptodome back here seems to have fixed the problem.

I know the cryptographic space in Python is a little strange, but it would be nice for maintenance purposes if there was a clearer tie between library marked as a requirement, and library being imported. If pyOpenSSL was being used for cryptography (through some indirect way to Crypto), we should make note of that in requirements.txt. It also seems like pyOpenSSL is unmaintained, and the recommendation is to replace it with cryptography. Maybe we ought to replace pycryptodome with cryptography; that would probably require some more research (see https://cryptography.io/en/latest/faq/#why-use-cryptography).

What do you think would be the appropriate course of action at this point?

Originally posted by @ssciolla in #1300 (comment)