Add CPM, bidder params, flag header in GreenbidsAnalyticsReporter

[EvgeniiMunin]

🔧 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?

We want to add the following info into analytics payload

• CPM from Bid, currency from BidResponse for each bidder
• bidder specific params from the BidRequest extension imp[].ext.prebid.bidder
• the custom flag header into HTTP POST call to distinguish between PBJS and PBS traffic on Greenbids Analytics Server side

The PR is based on #3096 and I will rebase it after the first one is merged

🧠 Rationale behind the change

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

🧪 Test plan

Have added givenPrebidNode with the bidder params into GreenbidsAnalyticsReporterTest so we can test the new payload.

🏎 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?