[config] Bug: Validation Logic for Configuration File Extension

[indraneel12]

ConfigurationParser.fromFile is currently case-sensitive to file extension. Expectedly, it should not have been case-sensitive like both of its upstream dependencies which are not restricted to accepting only case-sensitive file extensions:

...
if (filePath.endsWith('.json')) {
...
} else if (filePath.endsWith('.yaml') || filePath.endsWith('.yml')) {
...
throw UnsupportedError('Unsupported file extension: $filePath');

This bug results in a crash while loading external configurations (JSON or YAML) from, for example, configuration files with a fully uppercase filename.