before this change, we rely on the default-generated fmt::formatter
created from operator<<, but fmt v10 dropped the default-generated
formatter.
in this change, we
* define a formatter for `auth::resource` and friends,
* update their callers of `operator<<` to use `fmt::print()`.
* drop `operator<<`, as they are not used anymore.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#16765