[connector/elasticapm] Don't produce aggregation metrics if critical attributes are missing

[lahsivjar]

In certain cases, such as log-only ingestion, resource attributes like service.name can be missing, which defeats the purpose of aggregated metrics as they can't provide anything meaningful. For such events, we should put a condition in the signaltometrics to skip producing aggregated metrics.

• Revisit all attributes in signaltometrics config to identify attributes that are essential for the aggregated metrics to function. service.name is one such attribute.
• Update the signaltometrics config in elasticapm connector to not produce aggregated metrics if the identified attributes are missing in the incoming signal - this can be achieved by using conditions.

More context in this elastic-internal Slack thread.