Enhance serving evaluation endpoints (#595)

* Include metric_user_results in evaluation response, added eval json endpoint

* Remove query from response

* Utilize mapped inversed user id map to get original id in response

* Update serving test case to remove 'query' and add 'user_result' in response

* simplify user ID mapping

* Combined evaluation and evaluation_json endpoints

* Updated abort responses to show plaintext instead of html

* Added unit test cases

* Updated error response for empty data

* Added unit tests for provided data evaluation

* Update app.py

* Update test_app.py

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Co-authored-by: Quoc-Tuan Truong <tqtg@users.noreply.github.com>