OBJ_NAMED_PARAMS type works the same as OBJ type except it registers the object
keys to be accepted as top-level named-only RPC parameters. Generated
documentation also lists the object keys seperately in a new "Named arguments"
section of help text.
Named-only RPC parameters have the same semantics as python keyword-only
arguments (https://peps.python.org/pep-3102/). They are always required to be
passed by name, so they don't affect interpretation of positional arguments,
and aren't affected when positional arguments are added or removed.
The new OBJ_NAMED_PARAMS type is used in the next commit to make it easier to
pass options values to various RPC methods.
Co-authored-by: Andrew Chow <github@achow101.com>