IX: fix ix adapter handling of paapi config

[oronno]

🔧 Type of changes

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

✨ What's the context?

This is the fix of paapi auction config handling for IX Adapter as described in #3562

🧠 Rationale behind the change

Why did you choose to make these changes? Were there any trade-offs you had to consider?

This change aligns with how Index Exchange formats the auction configuration for the PAAPI response.

🔎 New Bid Adapter Checklist

• verify email contact works
• NO fully dynamic hosts
• geographic host parameters are NOT required
• NO 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?

🏎 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?