fix: enable FeatureHighAvailability if it is licensed (#10834)

fixes #10810

The tailnet coordinators don't depend on replicasync, so we can still enable HA coordinators even if the relay URL is unset.

The in-memory, non-HA coordinator probably has lower latency than the PG Coordinator, since we have to query the database, so enterprise customers might want to disable it for single-replica deployments, but this PR default-enables the HA coordinator.  We could add support later to disable it if anyone complains. Latency setting up connections matters, but I don't believe the coordinator contributes significantly at this point for reasonable postgres round-trip-time.

codersdk/deployment.go

@@ -95,6 +95,7 @@ func (n FeatureName) AlwaysEnable() bool {
 		FeatureExternalProvisionerDaemons: true,
 		FeatureAppearance:                 true,
 		FeatureWorkspaceBatchActions:      true,
+		FeatureHighAvailability:           true,
 	}[n]
 }