update beam search feature for interface with transformer model (#2855)
update beam search feature for interface with transformer model (#2855)

* update beam search for padding value and cache structure

* update python API for beam search

* add comments and update python layer

* modify comments format

* modify comments format

yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL