feat: add support for tls-auth, tls-crypt and tls-cryptv2

[clncy]

Checklist

• [x] I have read the contribution guidelines
• [ ] Iff you changed code related to services, or inter-service communication, make sure you update the diagrams in ARCHITECTURE.md.
• [x] Reference issue for this pull request: See https://github.com/ooni/minivpn/issues/75

Description

I've added support for the following control channel security protocols:

• tls-auth
• tls-crypt
• tls-cryptv2

Tested with ping against live openvpn servers, and added some very basic unit tests.