[FEATURE]Support Vega Overlay aggregations

[YANG-DB]

Is your feature request related to a problem?
For many vega components showing data-point graphs or time-series based aggregation, its interesting to compare the selected time range with previously time bucket -

• week over week
• day over day
• hour over hour

Do you have any additional context?

The next vega data attribute demonstrates how this can be achievable using the following data parts:

• rawdata-old: this is the older time based data aggregation query used to compare with and uses direct query to facilitate the 1 hour shift overlay.
• rawdata: this is the current time based data aggregation query
• flatdata: this is the combination of the two datasources (current + overlay)

Each data query is decorated with the time relevancy (Old,Current) transformation to indicate its origin

  "data": [
    {
      "name": "rawdata-old",
      "url": {
        "index": "otel-v1-apm-span-*",
        "body": {
          "query": {
            "bool": {
              "must": [
                "%dashboard_context-must_clause%"
                {
                  "range": {
                    "startTime": {
                      "%timefilter%": true,
                      "shift": 1,
                      "unit": "hour"
                    }
                  }
                }
              ]
              "must_not": [
                "%dashboard_context-must_not_clause%"
              ],
              "filter": [
                "%dashboard_context-filter_clause%"
              ]
            }
          }
          "aggs": {
            "services": {
              "terms": {
                "field": "serviceName",
                "size": 15
              },
              "aggs": {
                "time_buckets": {
                  "date_histogram": {
                    "field": "startTime",
                    "interval": {"%autointerval%": true},
                    "extended_bounds": {
                      "min": {"%timefilter%": "min"},
                      "max": {"%timefilter%": "max"}
                    },
                    "min_doc_count":0
                  },
                  "aggs": {
                    "duration": {
                      "avg": {
                        "missing": 0,
                        "script": {
                          "source": "!doc.containsKey('durationInNanos') || doc['durationInNanos'].empty ? 0 : doc['durationInNanos'].value / 1000000.0",
                          "lang": "painless"
                        }
                      }
                    }
                  }
                }
              }
            }
          },
          "size": 0
        }
      },
      "format": {"property": "aggregations.services.buckets"},
      "transform": [
        {"type": "formula", "expr": "'Old'", "as": "source"}
      ]
    },
    {
      "name": "rawdata",
      "url": {
        "index": "otel-v1-apm-span-*",
        "%context%": true,
        "%timefield%": "startTime",
        "body": {
          "aggs": {
            "services": {
              "terms": {
                "field": "serviceName",
                "size": 15
              },
              "aggs": {
                "time_buckets": {
                  "date_histogram": {
                    "field": "startTime",
                    "interval": {"%autointerval%": true},
                    "extended_bounds": {
                      "min": {"%timefilter%": "min"},
                      "max": {"%timefilter%": "max"}
                    },
                    "min_doc_count":0
                  },
                  "aggs": {
                    "duration": {
                      "avg": {
                        "missing": 0,
                        "script": {
                          "source": "!doc.containsKey('durationInNanos') || doc['durationInNanos'].empty ? 0 : doc['durationInNanos'].value / 1000000.0",
                          "lang": "painless"
                        }
                      }
                    }
                  }
                }
              }
            }
          },
          "size": 0
        }
      },
      "format": {"property": "aggregations.services.buckets"},
      "transform": [
        {"type": "formula", "expr": "'Current'", "as": "source"}
      ]
    },
    {
      "name": "flatdata",
      "source": ["rawdata", "rawdata-old"],
      "transform": [
        {
          "type": "flatten",
          "fields": ["time_buckets.buckets"],
          "as": ["val"]
        },
        {
          "type": "formula",
          "as": "timeInMs",
          "expr":"datum.val.key"
        },
        {
          "type": "formula",
          "as": "count",
          "expr":"datum.val.doc_count"
        },
        {
          "type": "formula",
          "as": "duration",
          "expr": "datum.val.duration.value == null ? 0 : datum.val.duration.value"
        },
        {
          "type": "formula",
          "as": "time",
          "expr": "timeFormat(utcParse(datum.val.key_as_string,'%Y-%m-%dT%H:%M:%S.%LZ'), '%B %d, %Y %H:%M')"
        }
      ]
    },
   ....
  ]

For rendering both the current data and old data the marks should consider the decorated source field

"marks": [
  {
    "type": "symbol",
    "from": {"data": "flatdata"},
    "encode": {
      "update": {
        "x": {"scale": "xScale", "field": "time"},
        "y": {"scale": "yScale", "field": "count"},
        "fill": {
          "condition": {"test": "datum.dataType === 'Old'", "value": "red"},
          "value": "blue"
        },
        "tooltip": {
          "signal": "{'Date': datum.time, 'Count': datum.count, 'Duration': datum.duration, 'Type': datum.dataType}"
        }
      }
    }
  }
]