Add Ecobee humidifier

[treylok]

Proposed change

Add ability to set the humidifier mode of an ecobee thermostat with a humidifier attached.

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

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request: Add ecobee humidifier home-assistant.io#16139

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.

The integration reached or maintains the following Integration Quality Scale:

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To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[probot-home-assistant]

Hey there @marthoc, mind taking a look at this pull request as its been labeled with an integration (ecobee) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[frenck]

Not stale, awaiting our review.

[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.

[bjpetit]

One comment/question regarding service schema.

[MartinHjelmare]

Looks great! Just one comment.

[treylok]

Should I close the documentation pull request since using the HumidifierEntity makes it irrelevant?

[MartinHjelmare]

We should at least add Humidifier to the ha_category and humidifier to the ha_platforms front matter YAML in the docs page.