Remove flag which disables authority discovery

[coriolinus]

@mxinden what is the reason authority discovery is still "optional"?

The authority discovery module was not mandatory thus far. The flag would allow a smoother feature roll out. I.e. first put it behind a feature flag then enable it by default but allow to disable it and eventually remove the possibility of disabling it.

Given that with the introduction of the overseer the authority discovery module becomes mandatory on authority nodes, I would suggest removing the flag entirely, always starting the authority discovery module on validator and sentry nodes. (The latter being deprecated paritytech/substrate#6845.)

Would that solve the issue at hand?

Originally posted by @mxinden in #1795 (comment)

[rphmeier]

I still believe that authority-discovery should be opt-in for your typical full node. We don't need the thousands of full nodes on the network all attempting to speak to authorities directly.

[rphmeier]

So I propose either a --enable-authority-discovery which --validator and Cumulus --collator imply, or for it to be an internal configuration that we enable only for validators and collators.

[mxinden]

We don't need the thousands of full nodes on the network all attempting to speak to authorities directly.

I agree.

or for it to be an internal configuration that we enable only for validators and collators.

This is my preference. As a side effect it would reduce the configuration surface and thus the operational complexity.

[bkchr]

or for it to be an internal configuration that we enable only for validators and collators.

I would also propose that we go this way.