Request Alias Bidder not using corebidder's bidderinfo

[pm-saurabh-narkhede]

As a part of this PR: https://github.com/prebid/prebid-server/pull/4019.

Request alias bidders are not retrieving the core bidder’s bidderInfo, resulting in the alias bidder defaulting to ORTB 2.5 and exiting further processing. Please refer for the specific changes: code reference

Eg. PubMatic bidder is configured with OpenRTB 2.6 protocol, BidRequest consist of two original bidders pubmatic and pubmatic-alias (request alias),

{
  "ext": {
    "prebid": {
      "aliases": {
        "pubmatic_alias": "pubmatic"
      }
    }
  }
}

Since pubmatic-alias fails to retrieve the bidderInfo with ORTB version 2.6 while creating bidrequests, the request is downgraded to ORTB 2.5. As a result, the PubMatic bidder endpoint will receive two requests:

pubmatic -> ORTB 2.6
pubmatic-alias -> ORTB 2.5.

Also, There are few instances in cleanOpenRTBRequests functions where we might need to send corebidder name instead of bidder aliases. Following is the list:

applyBidAdjustmentToFloor prepareUser

[bsardo]

This is an issue in PBS-Go but PBS-Java will double check if this issue exists.