Determine Correct Expansion of AuthenticationProvider interface for WebSocket Proxy

## Problem

The current `AuthenticationProvider` interface has the following method:

https://github.com/apache/pulsar/blob/fb7f14ceb04d612e456b2e5a834385ae3a97f68f/pulsar-broker-common/src/main/java/org/apache/pulsar/broker/authentication/AuthenticationProvider.java#L158-L174

The `HttpServletResponse` appears to have been introduced for multi-stage http authentication, which is only used by the `AuthenticationProviderSasl`:

https://github.com/apache/pulsar/blob/82237d3684fe506bcb6426b3b23f413422e6e4fb/pulsar-broker-auth-sasl/src/main/java/org/apache/pulsar/broker/authentication/AuthenticationProviderSasl.java#L229-L313

However, the WebSocket Proxy does not have access to an `HttpServletResponse`. It only has access to a `ServletUpgradeResponse`, as seen here:

https://github.com/apache/pulsar/blob/516437e370a711d48fe1d444a0c47e64e7cf2f4b/pulsar-websocket/src/main/java/org/apache/pulsar/websocket/AbstractWebSocketHandler.java#L91-L122

Therefore, the current API does not allow for multi-phased http authentication.

## Observations

`ServletUpgradeResponse` is a wrapper for `HttpServletResponse`, but it doesn't provide direct access. Does that mean we should add a new method to the `AuthenticationProvider` interface just for the WebSocket?

For now, the current state is that multi-stage auth is not supported in the WebSocket proxy. This technically aligns with the current limitation that multi-stage auth is not available in the regular pulsar proxy #19291.

Read AuthenticationProvider.java and AuthenticationProviderSasl.java to understand why HttpServletResponse is part of the interface. Then inspect AbstractWebSocketHandler.java and its ServletUpgradeResponse usage, and compare the limitation described in issue #19291. Done means establishing and documenting the correct interface direction for multi-stage authentication in the WebSocket proxy.

Written by the indexing model from the issue text.