Enable destination_project_quota for logs exporter (#579)

* Add destinationProjectQuota for logs exporter

* Add fixture for logs destination_project_quota

* Update readme

* Use empty string for map key when disabled

exporter/collector/README.md

@@ -322,8 +322,8 @@ By default, the exporter sends telemetry to the project specified by `project` i
 
 ### Multi-Project quota usage
 
-The `gcp.project.id` label can be combined with the `destination_project_quota` option to attribute quota usage to the project parsed by the label. This feature is currently only available
-for traces and metrics. The Collector's default service account will need `roles/serviceusage.serviceUsageConsumer` IAM permissions in the destination quota project.
+The `gcp.project.id` label can be combined with the `destination_project_quota` option to attribute quota usage to the project parsed by the label. This feature is available
+for traces, metrics, and logs. The Collector's default service account will need `roles/serviceusage.serviceUsageConsumer` IAM permissions in the destination quota project.
 
 Note that this option will not work  if a quota project is already defined in your Collector's GCP credentials. In this case, the telemetry will fail to export with a "project not found" error.
 This can be done by manually editing your [ADC file](https://cloud.google.com/docs/authentication/application-default-credentials#personal) (if it exists) to remove the `quota_project_id` entry line.

exporter/collector/integrationtest/testcases/testcases_logs.go

@@ -32,6 +32,14 @@ var LogsTestCases = []TestCase{
 		OTLPInputFixturePath: "testdata/fixtures/logs/logs_multi_project.json",
 		ExpectFixturePath:    "testdata/fixtures/logs/logs_multi_project_expected.json",
 	},
+	{
+		Name:                 "Multi-project logs with destination_project_quota enabled",
+		OTLPInputFixturePath: "testdata/fixtures/logs/logs_multi_project.json",
+		ExpectFixturePath:    "testdata/fixtures/logs/logs_multi_project_destination_quota_expected.json",
+		ConfigureCollector: func(cfg *collector.Config) {
+			cfg.DestinationProjectQuota = true
+		},
+	},
 	{
 		Name:                 "Logs with scope information",
 		OTLPInputFixturePath: "testdata/fixtures/logs/logs_apache_error_scope.json",