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graphql: Instrument field count and depth

Administrator requested to merge graphql-cost-v2 into main

Created by: ryanslade

This is v2 of our cost estimator, it's still a WIP and the idea is to deploy this in production so that we can get a sample of real world costs using this algorithm in Honeycomb.

This version tries to count the worst case number of fields returned by a query and treats all fields as having a cost of 1.

Additionally, it finds first and last parameters and uses them to multiply cost. For example, in the following query we always assume that 10 externalServices nodes will be returned and we therefore expect 10 occurences of displayName and webhookURL in the result:

query{
  externalServices(first: 10){
    nodes{
      displayName
      webhookURL
    }
  }
  somethingElse
}

When the estimator encounters inline fragments it evaluates the cost of each and pick the most expensive as we want the worst case.

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