validation on trigger side

[lixingwang]

Current behavior:
Today we already enabled validation on activity side but the trigger not
Expected behavior:
Enable schema validation on the trigger side as well.

What is the motivation / use case for changing the behavior?
Take rest trigger as an example: some of the cases that I need to validate the body before passing to action to make sure the body is expected.
Additional information you deem important (e.g. I need this tomorrow):