GPT2 one step beam search update with configuration support (#7425)
* check in early stop search as separate type
* rename to beam search configurations
* update do sample configuration flag help
* rename to configurable search step
* add option groups
* add more unit tests
Co-authored-by: Xiaoyu Liu <xiaoyu@xiaoyu-VM.z4vh1dzj5eoevgybsksdpz2izh.jx.internal.cloudapp.net>