Chunk streaming request bodies only

[mgyucht]

Changes

#138 changed the CommonsHttpClient implementation to use InputStreamEntity for all request bodies sent using the Java SDK. As a result, requests are sent with a Transfer-Encoding: chunked header, and the request body is chunked accordingly. However, the Databricks REST API only tolerates chunked requests for certain APIs; for others, it ignores the request body if Content-Length is not specified. Auth falls under that category, which caused #154.

To fix this, Request will keep track of string entities and input stream entities separately. Previously, Request had separate fields for the body and debugBody, but they were both always set, so it wasn't possible to distinguish between these two cases. Now, HTTP clients can have different behavior based on whether the request body can be fully materialized as a string or is lazily read as with input streams.

As part of this, I have removed SimpleHttpServer. This was used before we were sure whether it was possible to use the HttpServer built into the JDK. Now that we are confident that we can (see usage in ExternalBrowserCredentialsProvider.java), I've replaced it with HttpServer and a custom HttpHandler in FixtureServer (the only place where it is used now).

One other small change: I've updated the logging configuration and dependency for the cli auth demo app. This ensures that users can see debug output (which I used when debugging this).

Closes #154.

Tests

I've refactored FixtureServer to support more advanced validation on the HTTP requests sent by clients for testing purposes. Now, users can assert that a request has a specific method, path, headers, body, and check for headers that should not be present.

One downside of this change is that users need to call the .with() method once per API call, rather than one time, at the start of each test.

Unit tests cover both cases (request body should be chunked when specified as a String; request body should not be chunked when specified as an InputStream).

[mgyucht]

This used to be <InputStream>; I've changed it to (streamed body) in the debug log.

[mgyucht]

Not ClustersExt, but CommonsHttpClient

[mgyucht]

FixtureHandler?

[tanmay-db]

Right now, withEntity is only being called in POST / PUT and PATCH right? Is this pathway only for the PUT?

[mgyucht]

withEntity should be called for any HTTP methods that have a request body, i.e. POST/PUT/PATCH. GET/DELETE and other methods we may support in the future like HEAD/OPTIONS don't support request bodies, so we don't use this method.