[Feature Request] Add support to set annotations on the generated Service

[ammmze]

Is your feature request related to a problem? Please describe.
I'd like to be able to add an annotation to the Service that the EmqxBroker generates such as: coredns.io/hostname: "mqtt.example.com". This annotation specifically in my case causes coredns to add a DNS record resolving mqtt.example.com. to the ip address of the service.

Describe the solution you'd like
I think the spec.emqxTemplate.listener object on the EmqxBroker should support an annotations field which would then be used when generating the Service around here.

Describe alternatives you've considered
Alternatives would require that my load balancer ip is static and then manually adding the DNS record to core dns.
Or manually crafting a custom Service to run side by side with the one produced by the operator and effectively just leave the generated Service un-used.

[Rory-Z]

@ammmze
Cool ！we will include this in our development plans