Deprecate Plex YAML config

[jjlawren]

Breaking change

Plex configuration via YAML will be removed in 0.111.

Proposed change

Remove the YAML configuration option to reduce maintenance and support burdens. An alternative method to manually configure will be added to the Integration configuration flow in #34476.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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