There should be an error when resource attributes uniqueness assumption is violated

[eero-t]

This is continuation of v6 (Git version) issue #4283.

Expected behavior

Error of internal assumptions being violated for submitted resource attributes.

Actual behavior

No error, write_prometheus plugin reports multiple target_infos that have the same same service name + service instance ID pair:

$ curl --no-progress-meter 127.0.0.1:9999/metrics 
# HELP target_info Target metadata
# TYPE target_info gauge
target_info{job="unknown_service:collectd",instance="",dev_file="card0",host_name="icx-cp-1",pci_bdf="0000:4d:00.0",pci_dev="0x56c0"} 1
target_info{job="unknown_service:collectd",instance="",dev_file="card2",host_name="icx-cp-1",pci_bdf="0000:93:00.0",pci_dev="0x56c0"} 1
...
<the actual metrics>

Steps to reproduce

Plugin submits metrics that have the same name / labels, but a different resource.

However, although resources have different attributes, they have the same service name + service instance ID (e.g. "collectd" and "" or "pluginname"), instead of either or both of thembeing different for each resource.

This mistake is easy to do because:

• Everything worked fine when those same name & instance ID names were labels in every metric, instead of resource attributes
• Resource attribute being named "service.instance.id" does not really give the indication that it should contain ID for some other thing (e.g. device) than "service"