Support non-elasticsearch apis in suggestions

[erhathaway]

Thanks to @dearsaturn for suggesting this.

There should be the ability to config the Composer with an API for a non-elasticsearch source that supports the Elastic Composer Suggestion API. Then a suggestion can be configured to use this interface. The request should be put on the side effect queue like everything else to ensure debouncing etc...

Example use case:
Use Google Knowledge Graph to get suggestions
Use a different ES index to search text/keywords whose corresponding IDs can then be used in the Filter API