Uses MockWebServer instead of a docker container for servlet ITs

[codefromthecrypt]

What does this PR do?

This uses MockWebServer instead of a docker container for servlet ITs. In doing so, this simplifies the docker containers explicitly managed in our tests to one. That allows a simpler migration to the container jupiter extension in the future.

As this is test fixture only, I didn't check any checkbox as it isn't user-affecting enhancement or bug.

I chose okhttp MockWebServer..

• because we already have most classes in the classpath and a single version to manage via okhttp
• instead of com.sun.net.httpserver.HttpServer: as this is a dodgy type that only gets worse with new JREs
• instead of wiremock as this is doing simple dispatch, and MWS is more straightforward

Thoughts on the future enabled by this:

If we were to simplify to extensions, a better devex is possible, notably being able to run a single test, such as a method in SoapTestApp without running all other tests in a loop. This would be via other jupiter things such as @Nested, and in consideration of some limitations (in my experience, it is best to have a top-level class per docker image under test, vs a matrix, as it is easier to manage the sub-tests that way).

Checklist

• [ ] This is an enhancement of existing features, or a new feature in existing plugins
  • [ ] I have updated CHANGELOG.asciidoc
  • [ ] I have added tests that prove my fix is effective or that my feature works
  • [ ] Added an API method or config option? Document in which version this will be introduced
  • [ ] I have made corresponding changes to the documentation
• [ ] This is a bugfix
  • [ ] I have updated CHANGELOG.asciidoc
  • [ ] I have added tests that would fail without this fix
• [ ] This is a new plugin
  • [ ] I have updated CHANGELOG.asciidoc
  • [ ] My code follows the style guidelines of this project
  • [ ] I have made corresponding changes to the documentation
  • [ ] I have added tests that prove my fix is effective or that my feature works
  • [ ] New and existing unit tests pass locally with my changes
  • [ ] I have updated supported-technologies.asciidoc
  • [ ] Added an API method or config option? Document in which version this will be introduced
  • [ ] Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
• [ ] This is something else
  • [ ] I have updated CHANGELOG.asciidoc

[codefromthecrypt]

Thanks for the support @jackshirazi!