tools/net/ynl: add support for --family and --list-families

tools/net/ynl: add support for --family and --list-families

Add a --family option to ynl to specify the spec by family name instead
of file path, with support for searching in-tree and system install
location and a --list-families option to show the available families.

./tools/net/ynl/pyynl/cli.py --family rt_addr --dump getaddr

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250111154803.7496-1-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>