[chore] fix expected service name for prometheus e2e test

[bacherfl]

The metrics exposed by the collector's self monitoring prometheus endpoint at port 8888 contain a service_name="dynatrace-otel-collector" label, which is used for the resulting resource name.
Previously, apparently the job name from the prometheus config has been used for the service name:

        - job_name: opentelemetry-collector
          scrape_interval: 60s
          static_configs:
            - targets:
                - 127.0.0.1:8888

I'm not 100% sure yet why this has changed with the new upstream release, but my guess is that this is linked to the recent major version upgrade of the prometheus dependency: open-telemetry/opentelemetry-collector-contrib#36873

Update: It seems like since the prometheus version upgrade, the prometheus scrape manager will convert the service_name label provided by the collector self monitoring metrics to service.name, which is then set as a resource attribute by the prometheus receiver, overriding the previous service.name value determined by the job label