Support case insensitive bidder name in bidadjustmentfactors

[onkarvhanumante]

PR makes changes to support case insensitive bidder names in adjustment factors.

As shown below bidder name appnexus is known name to PBS. But APPNEXUS is unknown. Prior to PR changes PBS would have error out with unknown APPNEXUS bidder name messgae. PR has implemented insensitive bidder name comparison in bidadjustmentfactors

    {
       "imp": [
            {
               "ext": {
                   "prebid": {
                      "bidder": {
                          "APPNEXUS": { // sensitive appnexus
                          }
                       }
                    }
               }
            }
        ],
        ext: {
          "prebid": {
              "bidadjustmentfactors": {
                   "APPNEXUS": 1 // sensitive appnexus
               }
           }

partially resolves #2400