feat: implement boundary usage tracker and telemetry collection (#21716)

Implements telemetry for boundary usage tracking across all Coder
replicas and reports them via telemetry.

Changes:
- Implement Tracker with Track(), FlushToDB(), and StartFlushLoop() methods
- Add telemetry integration via collectBoundaryUsageSummary()
- Use telemetry lock to ensure only one replica collects per period

The tracker accumulates unique workspaces, unique users, and request
counts (allowed/denied) in memory, then flushes to the database
periodically. During telemetry collection, stats are aggregated across
all replicas and reset for the next period.

coderd/coderd.go

@@ -49,6 +49,7 @@ import (
 	"github.com/coder/coder/v2/coderd/appearance"
 	"github.com/coder/coder/v2/coderd/audit"
 	"github.com/coder/coder/v2/coderd/awsidentity"
+	"github.com/coder/coder/v2/coderd/boundaryusage"
 	"github.com/coder/coder/v2/coderd/connectionlog"
 	"github.com/coder/coder/v2/coderd/cryptokeys"
 	"github.com/coder/coder/v2/coderd/database"
@@ -266,6 +267,8 @@ type Options struct {
 	DatabaseRolluper *dbrollup.Rolluper
 	// WorkspaceUsageTracker tracks workspace usage by the CLI.
 	WorkspaceUsageTracker *workspacestats.UsageTracker
+	// BoundaryUsageTracker tracks boundary usage for telemetry.
+	BoundaryUsageTracker *boundaryusage.Tracker
 	// NotificationsEnqueuer handles enqueueing notifications for delivery by SMTP, webhook, etc.
 	NotificationsEnqueuer notifications.Enqueuer