OpenX - Add support for multi imp requests

[bukrain]

🔧 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?

Before this change, the OpenX bidder adapter has separated imps that contained only video format into it's separate bidRequest. This is no longer needed and we want to have multi imp requests even when there are imps with video format.

🧠 Rationale behind the change

Separating of video imps into their own separate bidRequests is no longer needed.

🧪 Test plan

Unit tests should be enough for this case.

🏎 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?