Add API to list supported configuration file extensions

[yybmion]

Summary

Add ConfigurationFactory.getActiveFileExtensions() and getSupportedExtensions() methods to allow external frameworks like Spring Boot to determine which configuration file formats are currently supported at runtime.

• Add abstract getSupportedExtensions() method to ConfigurationFactory
• Add static getActiveFileExtensions() method to aggregate results
• Implement getSupportedExtensions() in all ConfigurationFactory subclasses
• Add test coverage for new functionality

Example Usage

List<String> supportedExtensions = ConfigurationFactory.getActiveFileExtensions();
// Returns: ["xml", "json", "jsn", "properties"] (if Jackson available)
// Returns: ["xml", "properties"] (if Jackson missing)

closes #3775

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[github-actions]

Job	Requested goals	Build Tool Version	Build Outcome	Build Scan®
build-macos-latest	clean install	3.9.8	✅
build-ubuntu-latest	clean install	3.9.8	✅
build-windows-latest	clean install	3.9.8	✅

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