[gdebug] Openness to some maintenance?

The tool is potentially very useful but I suspect is underused (?) through a lack of familiarity and some complexity.

The current 'build' is slightly cumbersome and non-intuitive.

It would be useful to:

+ have a static `docker-compose.yaml`. This would be more explicit and it would e.g. enable `docker-compose ps` and `docker-compose logs ...` commands.
+ bump versions of Envoy to current and consider using the DockerHub container image directly
+ combine the build into e.g. Cloud Build (perhaps CircleCI, GitHub's equivalent).

The documentation could be improved slightly. It took me a couple of reads before I realized Envoy proxies the Angular site as well as the gRPC service.