Remote write compliance: TestRemoteWrite/otelcollector/InstanceLabel

[rakyll]

The OpenTelemetry collector is not passing https://github.com/prometheus/compliance/tree/main/remote_write
TestRemoteWrite/otelcollector/InstanceLabel.

=== CONT  TestRemoteWrite/otelcollector/InstanceLabel
    helpers.go:21:
        	Error Trace:	helpers.go:21
        	            				helpers.go:52
        	            				helpers.go:13
        	            				instance_label.go:26
        	            				main_test.go:101
        	            				main_test.go:65
        	Error:      	Should be true
        	Test:       	TestRemoteWrite/otelcollector/InstanceLabel
        	Messages:   	label 'instance' not found