B&A explicit API input to UDF indicating B&A(v.s. device)

[js345]

Today the signature of Ads provided UDF(generateBid) is the same for on-device and B&A and it more or less relies on the contents of inputs(whole ads objects or ad render ids) to distinguish between the different environments. With more payload optimization options such as omit-ads become available, it would be better that the execution worklet can provide an extra arg that indicates B&A.