New bidder & analytics adapter: Concert (attempt #2)

[jplhomer]

(resubmit of #5338)

Type of change

• New bidder and analytics adapter

Description of change

This PR adds the Concert bid adapter and analytics adapter to Prebid.

• test parameters for validating bids

  var adUnits = [
    {
      code: 'desktop_leaderboard_variable',
      mediaTypes: {
        banner: {
          sizes: [[1030, 590]]
        }
      }
      bids: [
        {
          bidder: "concert",
          params: {
            partnerId: 'test_partner'
          }
        }
      ]
    }
  ];
}

• contact email of the adapter’s maintainer: support@concert.io
• official adapter submission

Other information

• WIP until we can fix IE11 tests and update params

[jplhomer]

@msm0504 re-opened this PR to add the concert bidder and analytics adapter!

• Addressed your concerns about gzipping 👍
• Our server should now be returning bids for the test_partner parameters provided in the description
• The IE11 error is fixed - though CircleCI failed on an unrelated adapter timeout - and I can't trigger a re-run manually.