fix(targetingFlags): targeting flags are only present in the request if the user explicitly specifies them

[AbrahamArmasCordero]

https://github.com/prebid/prebid-mobile-android/issues/780 new changes have been applied from https://github.com/prebid/prebid-mobile-android/issues/780#issuecomment-2220177948

Hope this can be included in prebid, and sorry for the inconveniences

[jsligh]

Please add unit tests around this feature.