Add UniFi Uptime sensor

[timkoers]

Added the UniFi uptime data as a sensor. Untested.

Proposed change

New sensor feature, the UniFi Uptime time.

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

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:

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

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 @Kane610, mind taking a look at this pull request as its been labeled with an integration (unifi) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[Kane610]

You should put this in draft state until it is ready for review

[Kane610]

Other things expected prior to approval:
Add option in options flow to enable/disable this
Add option property to controller class with default being disabled
Add tests

[MartinHjelmare]

If it's a single sensor the enabling/disabling can be done via the standard entity options already.

[Kane610]

It's per client so potentially a lot of entities

[timkoers]

@MartinHjelmare and @Kane610 I think everything should be fixed now!

[Kane610]

Nearly there! Smaller things left. Please also add a test to comply with the coverage comment; verify that the same client gets added twice

[timkoers]

Nearly there! Smaller things left. Please also add a test to comply with the coverage comment; verify that the same client gets added twice

I've added the test that covers the uncovered line, including homeassistant/components/unifi/sensor.py#L58.

[timkoers]

👍

[MartinHjelmare]

Looks good!

Code owner should approve before merge.

[MartinHjelmare]

Docs should be updated:
https://www.home-assistant.io/integrations/unifi/#sensor

[timkoers]

All good, all of them have been fixed

[Kane610]

Awesome! Good job