rw-core should generate instance-id if not set

Currently the rw-core expects the instance-id of the container to be set via the command line arguments, else it defaults to a static default. Instead if the instance-id is not it could default to something like the HOSTNAME var, which under k8s is the pod name or even a dynamically generated value. Perhaps the instance-id parameter might recognize some key words:

• --instance-id=random == generate a uuid
• --instance-id=hostname == use the hostname
• --instance-id=<anything else> == take it literally

if nothing is specified it could default to random which is likely the most useful. Using the hostname just has some advantages for troubleshooting.

This is, of course, a moot point if the affinity router expects instance-ids to be reused when a rw-core crashes and restarts. This then gets much more interesting.