Improve viomi.vacuum.v8 (styj02ym) support (#1559)

This improves support for viomi vacuums and aims to make it available
for homeassistant without custom components (like
https://github.com/KrzysztofHajdamowicz/home-assistant-vacuum-styj02ym).
While this has been developed against "Mi Robot Vacuum-Mop P"
(viomi.vacuum.v8, styj02ym), it should work on all other viomivacuum
supported vacuums. Thanks to @KrzysztofHajdamowicz for providing access
to a test device :-)