Fix(GraphQL): Add support for repeatitive fields in aggregate query

[vmrajas]

Motivation:
Recently, support for Aggregation Queries was added to GraphQL. It was discovered later on that there existed a bug in Aggregate Queries. The bug is that adding a repetitive aggregate field generates an incorrect DQL query.
Example:

aggregateCountry {
    count
    cnt : count
}

generated a wrong DQL query and gave a malformed DQL query error.
This PR fixes this.

Testing:

1. Added tests to query_test.yaml .
2. Added tests to graphql/e2e/common .
   Fixes GRAPHQL-882

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This change is 

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[pawanrawal]

Reviewed 4 of 4 files at r1.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @abhimanyusinghgaur, @MichaelJCompton, @minhaj-shakeel, and @vmrajas)

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graphql/e2e/common/query.go, line 2929 at r1 (raw file):

				tmin : titleMin
				tmin_again : titleMin
				tmax: titleMax

Also, request this twice

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graphql/resolve/query_rewriter.go, line 193 at r1 (raw file):

	// Add selection set to mainQuery and finalMainQuery.
	isAggregateFieldVisited := make(map[string]bool)
	// isAggregateFunctionVisited stores if the aggregate function has been added or not.

function for a field has been added or not. So the map entries would contain keys as nameMin, ageMin, nameName, etc.

[vmrajas]

Reviewable status: 2 of 4 files reviewed, 2 unresolved discussions (waiting on @abhimanyusinghgaur, @MichaelJCompton, @minhaj-shakeel, and @pawanrawal)

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graphql/e2e/common/query.go, line 2929 at r1 (raw file):

Previously, pawanrawal (Pawan Rawal) wrote…

Also, request this twice

Done.

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graphql/resolve/query_rewriter.go, line 193 at r1 (raw file):

Previously, pawanrawal (Pawan Rawal) wrote…

function for a field has been added or not. So the map entries would contain keys as nameMin, ageMin, nameName, etc.

Done.