insights: add ability to extend timeout for aggregations

Created by: chwarwick

Adds the ability to extend the timeout for an aggregation to complete.

Also cleans up the returned messages for timeouts and adds a new returned reasonType for when an aggregation doesn't complete that holds the category of reason so that clients can use that to determine what action to take. The need for this is to give a clear signal to a client of why the aggregation failed and to be able to determine if it's possible to retry with the extended timeout.

Test plan

Updated unit tests request:

{
  searchQueryAggregate(query: "go\\s*(\\d\\.\\d+)", patternType: regexp) {
    aggregations(mode: CAPTURE_GROUP, limit: 10) {
      __typename
    
      ... on SearchAggregationNotAvailable {
        reason
        reasonType
      }
    }
  }
}

response:

{
  "data": {
    "searchQueryAggregate": {
      "aggregations": {
        "__typename": "SearchAggregationNotAvailable",
        "reason": "We couldn't provide an aggregation for this query. The query was unable to complete in the allocated time.",
        "reasonType": "TIMEOUT_EXTENSION_AVAILABLE"
      }
    }
  }
}

With timeout extension:

{
  searchQueryAggregate(query: "go\\s*(\\d\\.\\d+)", patternType: regexp) {
    aggregations(mode: CAPTURE_GROUP, limit: 2, extendedTimeout:true) {
      __typename
      ... on ExhaustiveSearchAggregationResult {
        groups {
          label
          count
          query
        }
        otherResultCount
        otherGroupCount
      }
      ... on SearchAggregationNotAvailable {
        reason
        reasonType
      }
    }
  }
}

response:

{
  "data": {
    "searchQueryAggregate": {
      "aggregations": {
        "__typename": "ExhaustiveSearchAggregationResult",
        "groups": [
          {
            "label": "1.16",
            "count": 493,
            "query": "/go\\s*(?:1\\.16)/"
          },
          {
            "label": "1.13",
            "count": 307,
            "query": "/go\\s*(?:1\\.13)/"
          }
        ],
        "otherResultCount": 2541,
        "otherGroupCount": 37
      }
    }
  }
}