SSL support on MQTT

[jonnor]

This is needed for user+password authentication to be secure, as they are otherwise in plaintext. This limits usage to secure private networks or completely public unauthenticated. Even in a (supposedly) trustworthy network one really should use encryption (defense-in-depth).

It could be that this already works, but need to verify and add documentation. Should also have some tests, at least in the runtime with some example participants.

• msgflo-nodejs
• noflo-runtime-msgflo
• msgflo-cpp
• msgflo-arduino
• msgflo-python
• msgflo-rust