Add option to read multiple desc files from multiple URLs

[gertz167]

Proposal

Currently there must be defined an additional sub directory named "grpc" in wiremock directory.

In our case the grpc desc files are part of a maven-third-party lib. That means we can not easily copy the desc files from a maven library to a subdirecty wiremock/grpc.

It would be great that the class GrpcExtensionFactory/GrpcHttpServerFactory supports URLs.
That would allow us to read the grpc desc files directly from the third-party-lib.

Here is an example how it would look like:

 @Test
    void testExecuteWiremockTest()  {
        // read myexample.com from third-party-maven-lib
        URL resource = this.getClass().getClassLoader().getResource("myexample.desc");
        System.out.println(resource.getFile());

        WireMockConfiguration options = WireMockConfiguration.options();
        options
            .dynamicPort()
            .extensions(new GrpcExtensionFactory(Collections.singletonList(resource)));
        wireMockServer = new com.github.tomakehurst.wiremock.WireMockServer(options);
        wireMockServer.start();
    }

References

No response

[gertz167]

I added the main change in PR #71