Add button/command for converting an ES JSON data structure to other langs

In particular, want to be able to convert from JSON to an assoc array in PHP for adding to PHP code.

I assume this would be useful for other languages also.

Start by locating the existing button or command entry points and the code that handles Elasticsearch JSON data structures. Define the supported output languages, beginning with a PHP associative-array representation, and consider how conversion results should be presented; done means the requested conversion is accessible and produces valid PHP output.

Written by the indexing model from the issue text.