Update NQ example (code & docs)

[anfelbar]

Towards OND-1483

[anfelbar]

As a follow up, I will fix the token authentication. It is supposed to work with github tokens but I will change that for JWT.

[anfelbar]

Try it against opal with

bazel run //java/com/engflow/notificationqueue:client  -- \      '--notification_queue_endpoint=grpcs://opal.cluster.engflow.com' '--queue_name=eventstore/lifecycle-events' \                                                    
      '--tls_certificate=/path/to/secrets/opal.crt' '--tls_key=/path/to/secrets/opal.key'

[vaibhav-shah]

Thank you Andres!!