Add support for URI's path prefix modification

[big-cir]

Overview

1. Added pathPrefix field and setter method to UriModifyingOperationPreprocessor
2. Added corresponding support in UriModifyingContentModifier

Related Issues

#945

Test

@Test
public void requestContentUriPathIsPreservedAndAddPathPrefix() {
    this.preprocessor
		    .removePort()
		    .pathPrefix("/addPathPrefix");
    OperationRequest processed = this.preprocessor
	    .preprocess(createRequestWithContent("The uri 'http://localhost:12345/foo/bar' should be used"));
    assertThat(new String(processed.getContent())).isEqualTo("The uri 'http://localhost/addPathPrefix/foo/bar' should be used");
}

@Test
public void responseContentUriPathIsPreservedAndAddPathPrefix() {
    this.preprocessor
		    .removePort()
		    .pathPrefix("addPathPrefix");
    OperationResponse processed = this.preprocessor
	    .preprocess(createResponseWithContent("The uri 'http://localhost:12345/foo/bar' should be used"));
    assertThat(new String(processed.getContent())).isEqualTo("The uri 'http://localhost/addPathPrefix/foo/bar' should be used");
}

[wilkinsona]

Thanks for PR. Unfortunately, I'm not sure that focussing solely on the path's prefix is the right approach as there may be a need to modify the path in other ways. I think we need to take a step back and consider exactly what modifications to support before looking at possible implementations. One option may be to support something like Spring Framework's UriComponentsBuilder. Another would be to allow the user to provide a UnaryOperator that's called with the current path and can return a new path modified in any way they require.