Allow 401 status without requiring HTTP authentication

[3dgiordano]

This pull request introduces a custom protocol handler to improve how HTTP 401 responses are handled in the BlazeMeter Jetty-based HTTP client. The main goal is to allow 401 responses without a WWW-Authenticate header (common with app-level authentication like JWT or API keys) to be returned as normal responses, matching the behavior of JMeter's HttpClient4. Previously, Jetty would treat these as protocol violations and fail the exchange. The change is validated with new unit tests.

Authentication protocol handler improvements:

• Added CustomWwwAuthenticationProtocolHandler as a replacement for Jetty's default handler, allowing 401 responses without WWW-Authenticate to be returned to the application instead of failing the request.
• Updated HTTP2JettyClient to install the custom handler on all internal HttpClient instances after startup. [1] [2] [3]

Testing and test infrastructure:

• Added a new test case to verify that a 401 response without a WWW-Authenticate header is handled as a normal 401 (not a protocol error), both with and without an authentication manager configured. [1] [2]
• Extended ServerBuilder to support a test path (SERVER_PATH_401_NO_WWW_AUTHENTICATE) that returns a 401 without the header, and updated the test server logic accordingly. [1] [2]

[Baraujo25]

Approved! I really liked the idea of having the jetty/ package ❤️ I feel like we are going to have a lot of mods inside-there 😅