Add sunrise and sunset to Darksky weather sensor

[fabaff]

Description:

Add sunrise and sunset to Darksky weather sensor.

Related issue (if applicable): fixes 85438

Pull request in home-assistant.io with documentation (if applicable): home-assistant/home-assistant.io#7917

Example entry for configuration.yaml (if applicable):

sensor:
  - platform: darksky
    api_key: !secret darksky_api
    forecast:
      - 0
    monitored_conditions:
      - sunrise_time
      - sunset_time

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io