Add server fuzzer

[AdamKorcz]

This PR adds a fuzz test for the servers ServeHTTP method.

The fuzzer controls several of the responses to also test the servers handling of odd responses.

The fuzzer creates a random http request and passes it to the servers ServeHTTP method. It does not check the error from the server and therefore primarily checks for bugs that will crash the server.

The fuzzer then proceeds to do the same for the Delta servers DeltaStreamHandler.

[valerian-roche]

Hey, thank you for your contribution

The Fetch API on the rest server is a rarely used piece of code of go-control-plane (as envoy and grpc usually use the sotw or delta gRPC APIs). Can you provide the motivation to add this on the REST API instead?