improve JS API to retrieve request and response #1962
Description
refer conversation here: #1861 (comment)
proposing the following for a start:
# get single header
* match karate.response.header('foo') == 'bar'
# get all header values by key
* match karate.response.headers('foo') == ['bar']
# same pattern for request
* match karate.request.header('foo') == 'bar'
# in future can add some helpers:
* match karate.response.body == 'success'
* match karate.request.method == 'PUT'