core: Google Assistant: Execute message does not always contain armLevel

Home Assistant release with the issue: 0.100.1 Last working Home Assistant release (if known): - Integration: Google Assistant Description of problem:

Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/components/google_assistant/smart_home.py", line 58, in _process
    result = await handler(hass, data, inputs[0].get("payload"))
  File "/usr/src/homeassistant/homeassistant/components/google_assistant/smart_home.py", line 168, in handle_devices_execute
    await entities[entity_id].execute(data, execution)
  File "/usr/src/homeassistant/homeassistant/components/google_assistant/helpers.py", line 294, in execute
    await trt.execute(command, data, params, challenge)
  File "/usr/src/homeassistant/homeassistant/components/google_assistant/trait.py", line 956, in execute
    if self.state.state == params["armLevel"]:
KeyError: 'armLevel'

Source: https://community.home-assistant.io/t/0-100-better-plex-bye-json-here-travel-time/141624/99?u=balloob

Looking at the sample execute messages from the docs, armLevel is indeed an optional parameter: https://developers.google.com/assistant/smarthome/traits/armdisarm#sample-execute-request-and-response

CC @engrbm87