GraphQL: Improve functional tests using GQL

Functional tests get complicated with many args. Use a Python GraphQL client to make quries

https://github.com/graphql-python/gql

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Migrated from T4554 (view on Phabricator)

mentioned in merge request !67 (closed)

assigned to @jayeshv

marked this issue as related to #4083

added GraphQL API priority:Normal labels

mentioned in commit 0f2eaba9

closed