tools: ynl: cli: introduce formatting for attr names in --list-attrs

tools: ynl: cli: introduce formatting for attr names in --list-attrs

It's a little hard to make sense of the output of --list-attrs,
it looks like a wall of text. Sprinkle a little bit of formatting -
make op and attr names bold, and Enum: / Flags: keywords italics.

Tested-by: Gal Pressman <gal@nvidia.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20260110233142.3921386-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>