[Feature] Specify secrets for listeners TLS certificates

[mdallaire]

Is your feature request related to a problem? Please describe.
There does not seem to be a way to use pre-existing certificates in kind: EmqxBroker

Describe the solution you'd like
Have an option to define an existing secret containing a TLS certificate for the secure ports

Describe alternatives you've considered
I can't find one right now in the information available on the kind: EmqxBroker. An other way of doing this would be to be able to specifiy an existing cluster issuer and dns names for automatic generation of the needed certs.

Related issue emqx/emqx#6337

[Rory-Z]

Hi, @mdallaire
It's a good question and we have plans to make it happen, it's already in our roadmap