Handle too long search input

[snyaggarwal]

Context: ES has a limit on number of characters in search request.

• ES throws RequestError(400, 'search_phase_execution_exception', 'failed to create query: input automaton is too large: 1001')
• OCL API throws 500

Tasks:

• [x] API to return 400 with error message
• [x] TB to stop user from search with error message on more than 400 characters.