docs: fix Home Assistant MQTT sensor JSON templates warnings

[longzheng]

Fixes #4247

More gracefully handles teslamate/cars/1/active_route topic JSON when the car is not routing, the json_attributes_template would cause a Home Assistant warning since we're trying to access properties on the JSON that aren't there.

MQTT topic active_route

{"error":"No active route available"}

Home Assistant logs

Oct 07 15:10:43 iot2 homeassistant[107792]: 2024-10-07 15:10:43.127 WARNING (MainThread) [homeassistant.components.mqtt.mixins] TypeError: Object of type LoggingUndefined is not JSON serializable rendering template for entity 'device_tracker.tesla_active_route_location', template: '{{ value_json.location | tojson }}' and payload: {"error":"No active route available"}
Oct 07 15:10:43 iot2 homeassistant[107792]: 2024-10-07 15:10:43.127 WARNING (MainThread) [homeassistant.helpers.template] Template variable warning: 'dict object' has no attribute 'destination' when rendering '{{ value_json.destination }}'
Oct 07 15:10:43 iot2 homeassistant[107792]: 2024-10-07 15:10:43.127 WARNING (MainThread) [homeassistant.helpers.template] Template variable warning: 'dict object' has no attribute 'energy_at_arrival' when rendering '{{ value_json.energy_at_arrival }}'
Oct 07 15:10:43 iot2 homeassistant[107792]: 2024-10-07 15:10:43.128 WARNING (MainThread) [homeassistant.helpers.template] Template variable warning: 'dict object' has no attribute 'miles_to_arrival' when rendering '{{ value_json.miles_to_arrival }}'
Oct 07 15:10:43 iot2 homeassistant[107792]: 2024-10-07 15:10:43.128 WARNING (MainThread) [homeassistant.helpers.template] Template variable warning: 'dict object' has no attribute 'minutes_to_arrival' when rendering '{{ value_json.minutes_to_arrival }}'
Oct 07 15:10:43 iot2 homeassistant[107792]: 2024-10-07 15:10:43.128 WARNING (MainThread) [homeassistant.helpers.template] Template variable warning: 'dict object' has no attribute 'traffic_minutes_delay' when rendering '{{ value_json.traffic_minutes_delay }}'

Also fix other template sensor errors mentioned in #4247 (comment) which are unrelated to the active route error but a similar issue where the template reference other MQTT sensor numeric values which may be invalid/unavailable, which causes a warning when trying to use math expressions on.

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[swiffer]

tested successfully here (updated mqtt_sensors.yaml, restarted home_assistant, no errors in logs).

[brianmay]

Looks good, but a bit puzzled about the changes from multiple to divide in some places.

[longzheng]

@JakobLichterfeld not sure why the CI failed, can you retry please

[JakobLichterfeld]

@JakobLichterfeld not sure why the CI failed, can you retry please

Yeah, GitHub Runners have been slow yesterday and caused lots of failures, not related to your PR. Today it runs fine.