If i’m right, i think you mean packages for configuring a room in one yaml file?
It’s not possible to configure the components AND the LL config in one file, but how about some project folder?
With packages, HA reads every yaml files in the packages folder, also in sub folders.
Example:
.homeassistant/packages/kitchen/kitchen.yaml for the components,
and
.homeassistant/packages/kitchen/ui_kitchen.yaml for the LL config,
and in the main ui_lovelace.yaml
title: Home
views:
- !include packages/kitchen/ui_kitchen.yaml
You have to use Lovelace YAML mode, the room has to be in it’s own view,
AND THIS IS ABSOLUTLY NOT TESTED (but i think it could work 
).