Refactor/simplify/modernize examples

[cer]

For example

• Use latest Eventuate starters
• See eventuate-tram-examples-basic-event-publisher and eventuate-tram-examples-basic-event-subscriber as the model

TODO:

• [ ] Refactor eventuate-tram-examples-basic-commands
• [ ] Refactor eventuate-tram-examples-basic-messaging
• [ ] Remove the broker-specific/in-memory modules

[cer]

See various commits in December that preceded https://github.com/eventuate-tram/eventuate-tram-core-examples-basic/commit/5c31d1bb43927e53e2e9888228d3e9e8e1f43777