Fix CLI option doc

[alexanderwerning]

The beat interval CLI option is beat-interval (dash), not beat_interval (underscore)

[thequilo]

This part of sacred seems to be a complete mess. Different CLI options use different naming conventions (_ or -). At least the documentation is correct for most of them (except beat-interval, which should be named heartbeat-interval in my opinion to match the name in the logs and code).

It would be great if we could unify all of them. The problem is that this would be a breaking change. Another idea would be to allow both - and _ for all CLI options.

[thequilo]

There is a check in the CLIOption that validates the option format: re.match(r"--[\w-]+\w$", long_flag). It is probably intended that the option only contains letters and -. But, \w also matches _, so matching --_ succeeds... That's a bug, but fixing it would be a breaking change

[thequilo]

There are also many other mistakes in the CLI option doc, e.g., the examples for print-config use print_config (which I'm sure was correct at some point).