common/ceph_json: dump bool using f->dump_bool()

common/ceph_json: dump bool using f->dump_bool()

as per https://www.json.org/json-en.html, JSON encodes bool as
"true" or "false", without the quotes. before this change, the quotes
are always added when encoding boolean values.

but this change is not backward compatible.

encode_json()'s bool overload is used by rgw. it uses JSONObj
defined in common/ceph_json.h to decode JSON-encoded structs.
and it does not differentiate bool from str when decoding a boolean
value despite that it could have check the "quoted" member variable
of JSONObj for validating the type of value. so we should be fine.

Fixes: https://tracker.ceph.com/issues/55189
Signed-off-by: Kefu Chai <tchaikov@gmail.com>