Add availability to opentherm_gw entities

[mvn23]

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 adds support for detecting availability of the gateway and/or sensor data.
So far only sensor and binary_sensor entities will report whether or not their data is included in the status report. The climate entity is now prepared for support as well, but it will require an update of the pyotgw library before it starts working. This update will be provided in a separate PR.

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:

• N/A 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:

• No score or internal
• 🥈 Silver
• 🥇 Gold
• 🏆 Platinum

[mvn23]

Failed tests seem unrelated. Can anyone confirm?

[basnijholt]

@mvn23, I have the same thing in #31967.

[MartinHjelmare]

Looks good! Just a small clean up.

[MartinHjelmare]

Suggested change

	self._available = status != {}
	self._available = bool(status)

[mvn23]

Thanks for the suggestion, I will take care of it tomorrow.

[mvn23]

Comment addressed and rebased on latest dev.
Failed tests seem to be related to TTS, which was not changed in this PR.

[MartinHjelmare]

Thanks!

[MartinHjelmare]

Test failures are unrelated as noted above. Merging.