client/authority-discovery: Allow to be run by sentry node (#5568)

* client/authority-discovery: Allow to be run by sentry node

When run as a sentry node, the authority discovery module does not
publish any addresses to the dht, but still discovers validators and
sentry nodes of validators.

* client/authority-discovery/src/lib: Wrap lines at 100 characters

* client/authority-discovery: Remove TODO and unused import

* client/authority-discovery: Pass role to new unit tests

* client/authority-discovery: Apply suggestions

Co-Authored-By: André Silva <[email protected]>

* bin/node/cli/src/service: Use expressions instead of statements

Co-authored-by: André Silva <[email protected]>