Use references in forked_daapd strings.json

[daveychu]

Proposed change

Use references in forked_daapd strings.json

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: Translations: Use references in config flow #40578
• 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
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• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
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  Updated by running python3 -m script.gen_requirements_all.
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[probot-home-assistant]

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

[uvjustin]

Looks fine. Can also change unknown_error and already_configured to
"unknown_error": "[%key:common::config_flow::error::unknown%]" and
"already_configured": "[%key:common::config_flow::abort::already_configured_device%]",

[springstan]

Thanks!

[MartinHjelmare]

The common key is just called unknown. Please replace that too.