Add derived measures to GraphQL

[shangyian]

Summary

This change makes the derived measures metadata from #1234 available to query via GraphQL. For example:

query ListNodes($namespace: String, $nodeTypes: [NodeType!], $tags: [String!], $editedBy: String, $after: String, $limit: Int) {
  findNodesPaginated(
    namespace: $namespace
    nodeTypes: $nodeTypes
    tags: $tags
    editedBy: $editedBy
    limit: $limit
    after: $after
  ) {
    edges {
      node {
        name
        type
        current {
          extractedMeasures {
            measures {
              name
              expression
              aggregation
              rule {
                type
              }
            }
            derivedQuery
            derivedExpression
          }
        }
      }
    }
    pageInfo {
      startCursor
      endCursor
      hasNextPage
      hasPrevPage
    }
  }
}

Test Plan

• PR has an associated issue: Surface metric metadata on aggregation #1223
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

N/A

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[agorajek]

We talked about having the derivedQuery and derivedExpression instead, but I assume we can change this later.