Add validation config and counters output for CDC Wonder

[abhishekjaisw]

This PR completes the onboarding of CDC Wonder NNDSS Infectious Weekly data into the Datacommons pipeline by adding validation guardrails.

Key changes:

1. Added Golden Data Validation: Includes baseline golden_data summaries and observations to run differential tests and safeguard against unexpected regression.
2. Fixed Missing References: Resolves mapping issues and flags missing references appropriately to pass strict validation rules.
3. Counters Output Generation: Adjusted the scripts in manifest.json to output processing metrics into the counters/ directory and configured the pipeline to persist them natively into the source_files destination on GCS.

[gemini-code-assist]

Code Review

This pull request introduces validation configuration and golden data files for the CDC Wonder NNDSS Infectious Weekly import. Specifically, it adds golden observations and summary reports, updates the import manifest to output counters and run validation, and defines validation rules in validation_config.json. The reviewer's feedback highlights critical path resolution issues in validation_config.json where golden and input file paths must be prefixed with ../../input1/ instead of ../../../../ to execute correctly in the validation environment. Additionally, the reviewer suggests ensuring the counters/ directory exists (e.g., via a .gitkeep file) to prevent runtime file-not-found errors when writing counters.