NoTask - Adding price structures endpoints

## Details
### Added
- brandwatch/pricestructures endpoints
  - GET brandwatch/pricestructures
  - POST brandwatch/pricestructures
  - DELETE brandwatch/pricestructures/{price_structure_id}

### Changed
- require and include new endpoints into /brandwatch

## Results
Ran rubocop and unit tests
- 95 files inspected, no offenses detected
- 41 examples, 0 failures