Support MOP running on the pulsar proxy

[thomaeschen]

Is your feature request related to a problem? Please describe.
Currently, In K8s environment we need to expose the MOP on broker to the LAN for clients using the MQTT protocols.

Describe the solution you'd like

It will be better to let the MOP run on the pulsar-proxy and redirect to the broker,hence we can (1)make the entire pulsar environment be more friendly to manage . (2)User could leverage to the same DNS name with different port number to send the request (3) the brokers could work as lightweight as original design

Describe alternatives you've considered

Additional context

[mattisonchao]

The MoP is the broker protocol handler. So, it can't move to the pulsar proxy.
However, maybe we can consider moving the MoP proxy to Pulsar-Proxy.

[thomasechen]

Great! Glad to hear if there is a good news

[mattisonchao]

Proposal is here: #756