this is a part of a series to migrating from `operator<<(ostream&, ..)`
based formatting to fmtlib based formatting. the goal here is to enable
fmtlib to print `auth::auth_authentication_options` and `auth::resource_kind`
without the help of fmt::ostream. and their `operator<<(ostream,..)` are
dropped, as there are no users of them anymore.
Refs #13245Closes#13460
* github.com:scylladb/scylladb:
auth: remove unused operator<<(.., resource_kind)
auth: specialize fmt::formatter<resource_kind>
auth: remove unused operator<<(.., authentication_option)
auth: specialize fmt::formatter<authentication_option>
fd817e199c