This is another follow-up from #7616. This makes the test options class
immutable and uses `@AutoValue` and `@AutoValue.Builder`. As a result, a
bunch of the configuration/setup code for these said options now flings
around a builder instance. This isn't great, but I think it's an
incremental improvement that can be seen in the `@BeforeAll
AbstractHttpClientTest.setupOptions()` method, where the immutable
options are (finally) instantiated.
As part of discussions #7616, the idea of trying to do a more piecemeal
approach came up. A reasonable ask.
This is the first step in refactoring the http client tests. It factors
out the `HttpClientResult` inner class of the `AbstractHttpClientTest`
so that this can be reused by new test framework later. It also factors
the relevant abstract methods in the abstract class to a new type
adapter, which will also be reused.
Co-authored-by: Mateusz Rzeszutek <mrzeszutek@splunk.com>