## Context
Adds support for multiple custom auth providers in custom-content
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## Summary by CodeRabbit
* **New Features**
* Added support for multiple custom sign-in providers via a new plural
configuration.
* Updated the sign-in page to render all configured custom provider
options while maintaining compatibility with the legacy single-provider
setting.
* Improved the custom provider button display to remove internal
prefixes from provider names.
* **Documentation**
* Updated the configuration schema, examples, and sample data to
document the new multi-provider setting.
* Marked the legacy single-provider configuration as deprecated in favor
of the plural option.
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* Init custom content hook
* Implement useCustomContent hook similarly to useIsFeatureEnabled, and implement extension of organization documents
* Attempt to type things nicely
* add test
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Co-authored-by: Jordi Enric <jordi.err@gmail.com>
Joshen Lim