Additional attribute for VideoParameters

[andriiginting]

Is your feature request related to a problem? Please describe.
Original request prebid/prebid-mobile-android#756
as stated in OpenRTB API Spec v2.5, we require to send a value to indicate whether the video object is skippable or not

Describe the solution you'd like
Based on OpenRTB API specification doc section Object: Video, one of the attributes is skip which indicates if the player allows the video to be skipped and battr which Blocked creative attributes.
Add a new attribute in to control skippable video objects with an integer value and add battr attribute with a list value

Describe alternatives you've considered

Additional context
I'm working in a new company and our partner asked to send this value through Prebid SDK