feat(entity): add connection status binary sensor to provide feedback in case of a disconnection

[palazzem]

Related Issues

• Closes #139

Proposed Changes:

This change adds a binary sensor as a feedback mechanism in case the device is not connected to the Cloud API. You can use it to know if the state that you see is up to date, to trigger automations, to send notifications.

Example:

Testing:

1. Add the binary sensor to your dashboard.
2. The sensor should be off in case of connection.
3. Disconnect your main unit (device).
4. The sensor should be triggered.

Extra Notes (optional):

This is a follow-up PR for #148. With both changes, we keep the previous state in case of disconnection to avoid triggering unwanted automations, but at the same time we provide a good feedback mechanism.

Checklist

• [x] Related issues and proposed changes are filled
• [x] Tests are defining the correct and expected behavior
• [x] Code is well-documented via docstrings

[coveralls]

Pull Request Test Coverage Report for Build 8112993791

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 4 of 4 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 93.964%

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Totals
Change from base Build 8112408535:	0.04%
Covered Lines:	673
Relevant Lines:	720

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💛 - Coveralls

[palazzem]

Merging as it's possible GitHub is experiencing some issues with their runners.