Support unloading/reloading Sonos

[jjlawren]

Proposed change

Support unloading of the config entry. Allows users to "reset" the integration if their network topology is changed during runtime or some unexpected scenario is encountered.

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:

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.

The integration reached or maintains the following Integration Quality Scale:

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• 🥇 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 @cgtobi, mind taking a look at this pull request as it has been labeled with an integration (sonos) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[bdraco]

Testing looks good
Even worked while I switched sources during the reload right after the entity went unavailable