Finish extracting time-tracking and dynamic-delay filters from ResponseOptions proto

After https://github.com/envoyproxy/nighthawk/pull/855/ is pushed through, these two filters now have their own configuration for starting up the filters, without any internal references to ResponseOptions.proto. However, the header override api still requires their fields to exist on ResponseOptions.proto, because the ResponseOptions proto is what is passed through the `x-nighthawk-test-server-config` header.

In order to move off this, we should:
1. Introduce three separate headers, one for each configuration (or one new header with three subsets of configuration). The current header will then become a legacy header and will issue warnings
2. Introduce a flag that makes only the new headers work
3. Remove the old header completely.