doc/netlink: Add a schema for netlink-raw families

This schema is largely a copy of the genetlink-legacy schema with the
following modifications:

 - change the schema id to netlink-raw
 - add a top-level protonum property, e.g. 0 (for NETLINK_ROUTE)
 - change the protocol enumeration to netlink-raw, removing the
   genetlink options.
 - replace doc references to generic netlink with raw netlink
 - add a value property to mcast-group definitions
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20230825122756.7603-3-donald.hunter@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>