Custom Charting tile processing ignores series entityType and selects filter based on metric definition entityType

[arthurpitman]

Describe the bug
Currently dashboard.CustomChartingTileProcessing ignores the entityType provided in the Custom Charting tile series and selects the filter based on metric definition entityType. While these are often identical, in cases where they are not this leads to no filter being applied.

Versions

• Dynatrace Service version: 0.17.1

To Reproduce
Get SLIs from a dashboard with a Custom Charting tile including a series with a custom entityType, e.g. SERVICE_KEY_REQUEST:

{
    "name": "Custom chart",
    "tileType": "CUSTOM_CHARTING",
    "configured": true,
    "bounds": {
        "top": 0,
        "left": 266,
        "width": 304,
        "height": 304
    },
    "tileFilter": {},
    "filterConfig": {
        "type": "MIXED",
        "customName": "Processing time;sli=processing_time;pass=<+10%,<5000",
        "defaultName": "Custom chart",
        "chartConfig": {
            "legendShown": true,
            "type": "TIMESERIES",
            "series": [
                {
                    "metric": "builtin:service.keyRequest.totalProcessingTime",
                    "aggregation": "AVG",
                    "type": "LINE",
                    "entityType": "SERVICE_KEY_REQUEST",
                    "dimensions": [
                        {
                            "id": "0",
                            "name": "dt.entity.service_method",
                            "values": [],
                            "entityDimension": true
                        }
                    ],
                    "sortAscending": false,
                    "sortColumn": true,
                    "aggregationRate": "TOTAL"
                }
            ],
            "resultMetadata": {}
        },
        "filtersPerEntityType": {
            "SERVICE_KEY_REQUEST": {
                "AUTO_TAGS": [
                    "keptnmanager"
                ]
            }
        }
    }
}

Observe that no filter is applied in the generated SLI.

Expected behavior
Filter is selected based on entityType from the series and included in the generated SLI.

Additional context
This issue is part of the cause for the behavior observed in #369