Add unavailable to Vera (#46064)

homeassistant/components/vera/__init__.py

homeassistant/components/vera/binary_sensor.py

homeassistant/components/vera/light.py

homeassistant/components/vera/manifest.json

homeassistant/components/vera/sensor.py

homeassistant/components/vera/switch.py

requirements_all.txt

requirements_test_all.txt

tests/components/vera/test_binary_sensor.py

tests/components/vera/test_climate.py

tests/components/vera/test_cover.py

tests/components/vera/test_light.py

tests/components/vera/test_lock.py

tests/components/vera/test_sensor.py

tests/components/vera/test_switch.py