ILMT support multiple different metrics single json array payload - like UMS does

Currently UMS supports not including metricName in the CR, and sending a single JSON array payload such that many metrics are mapped to the same mappingId, each with their own metricName in the payload we send.
Example payload:
[{"mappingId": "SOME_UNIQUE_ID",
   "instances": [{
       "metrics": [{
           "metricName": "Metric1Name",
           "measurementTimestamp": "2026-02-19T15:30:00.000Z",
           "metricQuantity": 42
         },{
           "metricName": "Metric2Name",
           "measurementTimestamp": "2026-02-19T15:30:00.000Z",
           "metricQuantity": 7
         }
       ]}] }]
This is beneficial as it allows us to use a single CR with even 100 unique metrics. It also means every time we add a new metric, we don't have to update the CR.

When we try to implement similar in ILMT, we get an error that metricName is required in the .ums.meta.json file
This means we cannot send the same payload in ILMT as we do for UMS.

Our implementation is we aggregate the metric data on our end and then send the payload quantities with processing: LAST. 

We do not want to go with the approach of having one metricName ex: INSTANCE_COUNT with all our many dynamic metrics(changing day to day) just as static metric metadata in groupBy as then the individual metrics would not be visible in SWC, and also it would restrict us to not being able to pass metadata per unique metric. 

This is something UMS supports.