Ability to support custom header sizes for HTTP Requests

**Is your enhancement request related to a problem? Please describe.**
Currently, Pulsar broker and proxy do not support use cases involving Http requests with a header size of more than 8k. Certain applications require large header sizes to support features such as custom authentication with Pulsar.

**Describe the solution you'd like**
The HTTP Request header size for Pulsar broker and proxy should be configurable. This will enable applications that require large header sizes to set values as per their specific requirements.

Start by locating the HTTP server configuration used by the Pulsar broker and proxy, then find where the current 8k request-header limit is set and whether each component has coverage for it. Define how users configure the limit for both components, add or update tests for larger headers and the default behavior, and verify the setting works for broker and proxy requests.

Written by the indexing model from the issue text.