Add component test framework

[Kaliumhexacyanoferrat]

As the developer of a web application, I would like to test my application using component tests.

Example

[TestClass]
public sealed class MyTests
{

    [TestMethod]
    public async Task MyTest()
    {
        // setup the project
        var project = ...;

        using var host = TestHost.Run(project);

        var request = host.GetRequest("/myfunc");

        using var response = await host.GetResponse(request);

        Assert.AreEqual(HttpStatusCode.OK, response.StatusCode);
    }

}

Acceptance criteria

• The functionality is implemented in a new project (e.g. GenHTTP.Testing)
• The test host allocates an available port when started
• The hosts allows to easily create requests and read responses
• Tests can be executed in parallel

[Kaliumhexacyanoferrat]

Additional tasks:

• Update documentation after release
• Update project templates after release
• Update MockH and GenHTTP.Gateway to use this framework after release