knative - form data - support web action form data

[pritidesai]

OpenWhisk web actions may receive URL encoded form data application/x-www-form-urlencoded as input in addition to standard application/json.

V.S. Knative web actions only accepts application/json data. We need to find a way using build file to configure input data, may be with arguments:

https://github.com/mrutkows/openwhisk-knative-build/blob/master/runtimes/javascript/tests/webactionhelloworld/build.yaml.tmpl#L14