Graphql-engine: support column operators _ceq in graphql api

[coco98]

https://docs.hasura.io/1.0/graphql/manual/api-reference/graphql-api/query.html#columnexp

(Via @jrhicks on discord)

[0x777]

@coco98 They are not supported in the graphql interface yet.

[lexi-lambda]

@0x777 Why is this hard?

[ice0136]

I'd like to upvote this feature. Currently I have to use sequelize and APIs to accomodate this all-to-common need.
select * from table where column1 > column2;
... wish there was a way to do this in graphql where clause.

[avimoondra]

Another example where ceq would be useful in query - https://stackoverflow.com/questions/61674263/compare-two-fields-in-graphql-hasura