User metadata with nested JSON not properly indexed

[max-zilla]

https://github.com/clowder-framework/clowder/blob/develop/app/util/SearchUtils.scala#L69

This attempts to flatten JSON contents into an array when duplicate keys are encountered. but doesn't work if the JSON is nested.
The logic seems to assume the JSON will only be Metadata Definitions (i.e. from GUI). the cat:extractor user doesn't do any of this. Needs to either wait until it reaches leaf node of metadata to do the array-ification, or find another way to index multiple occurrences of a Metadata Definition.