Disable unit counters, as they break prometheus

See open-telemetry/opentelemetry-dotnet-contrib/issues/1617

Boot.Metrics/BootMetricsPluginStartup.cs

@@ -46,7 +46,7 @@ public void ConfigureServices(IServiceCollection services)
             .AddMeter("Boot.Metrics.*")
 
             // Export to Prometheus
-            .AddPrometheusExporter());
+            .AddPrometheusExporter(o => o.DisableTotalNameSuffixForCounters = true));
 
         // tracing omitted because that'd require adding spans in Impostor
     }