feat: add boundary usage tracking database schema and tracker skeleton (#21670)

feat: add boundary usage telemetry database schema and RBAC

Adds the foundation for tracking boundary usage telemetry across Coder
replicas. This includes:

  - Database schema: `boundary_usage_stats` table with per-replica stats
    (unique workspaces, unique users, allowed/denied request counts)
  - Database queries: upsert stats, get aggregated summary, reset stats,
    delete by replica ID
  - RBAC: `boundary_usage` resource type with read/update/delete actions,
    accessible only via system `BoundaryUsageTracker` subject (not regular
    user roles)
  - Tracker skeleton + docs: stub implementation in `coderd/boundaryusage/`

The tracker accumulates stats in memory and periodically flushes to the
database. Stats are aggregated across replicas for telemetry reporting,
then reset when a new reporting period begins. The tracker implementation
and plumbing will be done in a subsequent commit/PR.

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

coderd/rbac/object_gen.go

@@ -63,6 +63,15 @@ var (
 		Type: "audit_log",
 	}
 
+	// ResourceBoundaryUsage
+	// Valid Actions
+	//  - "ActionDelete" :: delete boundary usage statistics
+	//  - "ActionRead" :: read boundary usage statistics
+	//  - "ActionUpdate" :: upsert boundary usage statistics
+	ResourceBoundaryUsage = Object{
+		Type: "boundary_usage",
+	}
+
 	// ResourceConnectionLog
 	// Valid Actions
 	//  - "ActionRead" :: read connection logs
@@ -417,6 +426,7 @@ func AllResources() []Objecter {
 		ResourceAssignOrgRole,
 		ResourceAssignRole,
 		ResourceAuditLog,
+		ResourceBoundaryUsage,
 		ResourceConnectionLog,
 		ResourceCryptoKey,
 		ResourceDebugInfo,