Monitoring: the fork's acceptance suite (MON-1 to MON-31)

system::monitoring::monitoring_tests covers the defaults, metric
sampling, the Prometheus gauges, trace history over SMTP and LMTP
(probe sessions skipped, no raw I/O), trace destroy, indexTelemetry off,
live metrics and live tracing with their tokens and stream limit,
alerts by event and by email, and tenant admins refused. Also removes a
leftover enterprise-only attribute on the Prometheus counters loop,
which would have dropped counters from an enterprise-feature build.

crates/common/src/telemetry/metrics/prometheus.rs

@@ -16,9 +16,6 @@ impl Server {
     pub async fn export_prometheus_metrics(&self) -> trc::Result<String> {
         let mut metrics = Vec::new();
 
-
-        #[cfg(not(feature = "enterprise"))]
-
         // Add counters
         for counter in Collector::collect_counters() {
             let mut metric = MetricFamily::default();