Honor Otel Service Name

Telemetry resource now honors OTEL_SERVICE_NAME and OTEL_RESOURCE_ATTRIBUTES

Terragrunt previously hardcoded the service.name resource attribute to terragrunt for every emitted trace and metric, ignoring the standard OpenTelemetry environment variables. Multiple Terragrunt invocations could not be distinguished in an OpenTelemetry backend without an intermediate collector to rewrite the attribute.

The resource is now composed via resource.New with WithFromEnv() placed after Terragrunt's defaults, so OTEL_SERVICE_NAME and OTEL_RESOURCE_ATTRIBUTES are honored on every span and metric. Per the OpenTelemetry specification, OTEL_SERVICE_NAME takes precedence over a service.name entry in OTEL_RESOURCE_ATTRIBUTES. The default service.name remains terragrunt when neither variable is set.