Configure Fly.io example addresses with entrypoint script

[catflydotio]

The old entrypoint script was setting the gossip address OK for the agent to start up, but env vars set in a script don't persist outside that script run, so then the actual address was invisible from a shell.

The fly-local-6pn line in config.toml isn't valid, so you get invalid socket address syntax trying to run a comand like corrosion reload.

This PR writes the actual 6pn address into the config file for gossip address, and puts the app name into the bootstrap address so you don't have to remember to change that from corrosion2 on deployment.