Add weather platform to template domain

[dgomes]

Proposed change

Template domain has many platforms, but not weather until now.
The use case is simple: you have separate sensors for temperature/humidity/etc and you want to combine them into a single entity. To top this use case, you can incorporate the forecast from a nearby location provided by another weather integration.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example entry for configuration.yaml:

# Example configuration.yaml

weather:
  - platform: template
    name: teste
    condition_template: "sunny"
    temperature_template: "{{ states('sensor.temperature') | float}}"
    humidity_template: "{{ states('sensor.humidity')| float }}"

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request: Add template Weather provider home-assistant.io#16681

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

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

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

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[MatthewFlamm]

Also according to the dev docs, the condition and temperature forecasts are required. One really nice use case for this template is to use the forecasts and current condition from an existing weather integration and the current temperature from a local temperature sensor.

[dgomes]

Thank you for the feedback! I've update the PR description :)

[MatthewFlamm]

Since I commented here, I found out that the underlying weather entity requires the integration to implement the humidity method in contrast to the developer documentation. It is now unclear what is the expectation. Thanks for linking this PR to the issue.

[github-actions]

There hasn't been any activity on this pull request recently. This pull request has been automatically marked as stale because of that and will be closed if no further activity occurs within 7 days.
Thank you for your contributions.

[gsdevme]

This looks handy for anyone wanting to bring in MQTT sensors and populate the weather domain to use the lovelace card also as I noticed there isnt a MQTT Weather component yet.

[bdraco]

Coverage looks good
homeassistant/components/template/weather.py 91 0 100%

[bdraco]

LGTM, just needs docs.

[bdraco]

LGTM. Thanks!