Update docs to reflect everywhere wskdeploy does interpolation on manifest values

It became apparent to me that we have not kept the docs current as to what values in the manifest now support interpolation (and more could!).

This involves going through the manifest parser: https://github.com/mrutkows/openwhisk-wskdeploy/blob/master/parsers/manifest_parser.go

and look for all places where a value is extracted via the "InterpolateStringWithEnvVar()" function and document it here:
https://github.com/apache/openwhisk-wskdeploy/blob/master/docs/wskdeploy_interpolation.md