Load all feature flag with no label when there is no selector specified

[zhiyuanliang-ms]

#157

[zhiyuanliang-ms]

This PR need to be merged before stalizing v2

[Copilot]

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src/AzureAppConfigurationImpl.ts:902

• The error message on line 902 should be updated to reflect the new behavior of loading all feature flags with no label when no selectors are specified.

return [{ keyFilter: `${featureFlagPrefix}${KeyFilter.Any}`, labelFilter: LabelFilter.Null }];