Add event tracking data to sessions cube

To avoid joining the sessions cube to the TrackedEvents cube, we can add those columns/dimensions directly to the sessions cube.

Example query:

{
  "measures": [
    "Sessions.count"
  ],
  "timeDimensions": [
    {
      "dimension": "Sessions.startAt"
    }
  ],
  "order": {
    "Sessions.count": "desc"
  },
  "dimensions": [
    "Sessions.parsedUaUaFamily"
  ]
}