Document that Logger reflects Feign's Request, not the wire request

[ChrisJr404]

Adds a note to the Logger class javadoc explaining that request logging reflects the Request that Feign builds, which can differ from what the underlying Client actually sends. The default HttpURLConnection based Client drops headers the JDK treats as restricted, so a header can show up in the log without being on the wire. Closes #2682.

[velo]

Thanks for adding this — the clarification about Logger reflecting Feign's Request rather than the wire request is a genuinely useful thing to document, and I confirmed the core claim is accurate (Logger.logRequest is called in SynchronousMethodHandler before client.execute, so the request logged really can differ from what goes over the wire).

Two things before merging:

1. The doc points at {@link Client.Default}, but that class is @Deprecated (see its javadoc: "use DefaultClient instead"). Feign.Builder actually defaults to new DefaultClient(...), and the restricted-header-dropping behavior you're describing lives in DefaultClient (e.g. the Content-Length: 0 handling around line 228), not in the deprecated wrapper. Please repoint the {@link} to DefaultClient.

2. Consider moving the detailed JDK-specific rationale (the HttpURLConnection restricted-headers behavior, sun.net.http.allowRestrictedHeaders, specific header names) onto DefaultClient's own class javadoc, with a short pointer from Logger's doc ("see {@link DefaultClient} for a concrete example"). That keeps the detail next to the code that actually causes it, where someone touching DefaultClient's header handling would be looking.

Happy to merge once the class reference is fixed.