HA template sensor proposal

template_sensor_proposal.yaml

## Working example

- platform: template
  sensors:
    person_count:
      friendly_name: "Number of Person at home"
      unit_of_measurement: 'person'
      entity_id: 
        - person.person1
        - person.person2
        - person.person3
        - person.person4
      value_template: >-
        {{ states.person|selectattr('state', 'equalto', 'home')|list|length }}
        
## Not working example

- platform: template
  sensors:
    person_count:
      friendly_name: "Number of Person at home"
      unit_of_measurement: 'person'
      entity_id: >-
        {{ states.person | map(attribute='entity_id') | list }}
      value_template: >-
        {{ states.person|selectattr('state', 'equalto', 'home')|list|length }}