Upgrade osm-osw-reformatter to 0.3.7 - #93

## Dev Board Ticket

- https://dev.azure.com/TDEI-UW/TDEI/_workitems/edit/4066
- https://dev.azure.com/TDEI-UW/TDEI/_workitems/edit/4069
- https://dev.azure.com/TDEI-UW/TDEI/_workitems/edit/4070

## Changes
- Upgraded `osm-osw-reformatter` to `0.3.7`
- Added formatter warnings to standard formatter response payloads
- Added formatter warnings to on-demand formatter response payloads
- Added `warnings` support to `ValidationResult`, `OSWValidationData`, and on-demand `ResponseData`
- Updated README and sample response config to document `warnings`
- Added unit coverage for warning propagation and response serialization

## Testing
```
.venv/bin/python -m pytest tests/unit_tests
.........................................................................
Ran 73 tests

OK
```