public String getMetricsAsString(List<VespaService> services) {
        MetricStringBuilder msb = new MetricStringBuilder();
        for (VespaService service : services) {
            msb.service = service;
            service.consumeMetrics(msb);
        }
        return msb.toString();
    }
Returns a string representation of metrics for the given services;
a space separated list of key=value.
metrics-proxy/src/main/java/ai/vespa/metricsproxy/core/VespaMetrics.java