Produce message using REST API through Proxy

**Is your enhancement request related to a problem? Please describe.**
Since Pulsar 2.9.X, the pulsar system is able to produce message directly to the broker from the REST client. It is more convenient and safety to let the user to produce the message using REST client to the proxy instead directly to the broker.

**Describe the solution you'd like**
The REST client could send the message to the proxy and the proxy redirect the request to the broker to produce a message

**Describe alternatives you've considered**
1. Create a reverse proxy in the K8s to redirect the message from outside to the broker-service which is inside the k8s
2. Expose the broker URL to the outside of the k8s

**Additional context**

No files, tests, or entry points are named. Start by locating the existing REST message-production path and the proxy-to-broker request handling, then determine how the proxy should accept and forward the request; done means a REST client can produce through the proxy without exposing the broker directly.

Written by the indexing model from the issue text.