Draft: Add new endpoint to convert OPA query to ElasticSearch query

LH Hon [ExxonMobil]requested to merge
hon_poc_opa_elasticsearch into master

License check: github.com/open-policy-agent/rego-python = apache license 2.0 - OK github.com/elastic/elasticsearch-dsl-py = apache license 2.0 - OK

Edited by LH Hon [ExxonMobil]

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