Enable Optional Encryption Without CA_Cert

[krkeegan]

Proposed change

Adds the following enable setting to config.yaml

mqtt:
  encryption:
    enable: False

Previously encryption was enabled by setting the ca_cert value. But this is not necessary if your servers cert is from a trusted authority such as Let's Encrypt.

I added a deprecation warning to the documentation, but for the time being if ca_cert is set encryption will continue to be enabled even if enable: False. This will only affect users who have enabled encryption previously and now attempt to disable it with encryption: False. Since I suspect basically no one updates their config files with settings that are added in later, I doubt this will ever be an issue.

Also encryption seems to be a little used feature.

Additional information

• This PR fixes or closes issue: fixes CA_Cert is Not Required for TLS Connection to MQTT #535

Checklist

• The code change is tested and works locally.
• Local tests pass.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated