Nativo: Add optional placementId parameter

[rafataveira]

This pull request adds integration test coverage for the Nativo bidder adapter. It introduces a JSON schema for validating Nativo adapter parameters, a new integration test class, and the corresponding test request and response fixtures.

Integration test for Nativo adapter:

• Added a new integration test class NativoTest to verify that the OpenRTB auction endpoint responds correctly with bids from the Nativo bidder. The test uses WireMock to stub the Nativo exchange and validates the auction response.

Test fixtures for Nativo integration:

• Added test request and response JSON files for the auction (test-auction-nativo-request.json, test-auction-nativo-response.json) and for the Nativo bid exchange (test-nativo-bid-request.json, test-nativo-bid-response.json). [1] [2] [3] [4]

Schema validation:

• Introduced a new JSON schema file nativo.json to define and validate the parameters accepted by the Nativo adapter.

🔧 Type of changes

• new bid adapter
• bid adapter update
• new feature
• new analytics adapter
• new module
• module update
• bugfix
• documentation
• configuration
• dependency update
• tech debt (test coverage, refactorings, etc.)

✨ What's the context?

Adding optional property "placementId" to Nativo Adapter.

🧠 Rationale behind the change

We have already been using this property but it wasn't correctly documented into the adapter.

🔎 New Bid Adapter Checklist

• verify email contact works
• NO fully dynamic hostnames
• geographic host parameters are NOT required
• direct use of HTTP is prohibited - implement an existing Bidder interface that will do all the job
• if the ORTB is just forwarded to the endpoint, use the generic adapter - define the new adapter as the alias of the generic adapter
• cover an adapter configuration with an integration test

🧪 Test plan

How do you know the changes are safe to ship to production?
Yes, just adding new optional property

🏎 Quality check

• Are your changes following our code style guidelines?
• Are there any breaking changes in your code?
• Does your test coverage exceed 90%?
• Are there any erroneous console logs, debuggers or leftover code in your changes?