feat(coderd): batch agent stats inserts (#8875)

This PR adds support for batching inserts to the workspace_agents_stats table.
Up to 1024 stats are batched, and flushed every second in a batch.

coderd/coderd.go

@@ -43,6 +43,7 @@ import (
 	"github.com/coder/coder/buildinfo"
 	"github.com/coder/coder/coderd/audit"
 	"github.com/coder/coder/coderd/awsidentity"
+	"github.com/coder/coder/coderd/batchstats"
 	"github.com/coder/coder/coderd/database"
 	"github.com/coder/coder/coderd/database/dbauthz"
 	"github.com/coder/coder/coderd/database/pubsub"
@@ -160,6 +161,7 @@ type Options struct {
 	HTTPClient *http.Client
 
 	UpdateAgentMetrics func(ctx context.Context, username, workspaceName, agentName string, metrics []agentsdk.AgentMetric)
+	StatsBatcher       *batchstats.Batcher
 }
 
 // @title Coder API
@@ -180,6 +182,8 @@ type Options struct {
 // @in header
 // @name Coder-Session-Token
 // New constructs a Coder API handler.
+//
+//nolint:gocyclo
 func New(options *Options) *API {
 	if options == nil {
 		options = &Options{}
@@ -288,6 +292,10 @@ func New(options *Options) *API {
 		options.UserQuietHoursScheduleStore.Store(&v)
 	}
 
+	if options.StatsBatcher == nil {
+		panic("developer error: options.StatsBatcher is nil")
+	}
+
 	siteCacheDir := options.CacheDir
 	if siteCacheDir != "" {
 		siteCacheDir = filepath.Join(siteCacheDir, "site")
@@ -462,6 +470,8 @@ func New(options *Options) *API {
 	cors := httpmw.Cors(options.DeploymentValues.Dangerous.AllowAllCors.Value())
 	prometheusMW := httpmw.Prometheus(options.PrometheusRegistry)
 
+	api.statsBatcher = options.StatsBatcher
+
 	r.Use(
 		httpmw.Recover(api.Logger),
 		tracing.StatusWriterMiddleware,
@@ -994,6 +1004,8 @@ type API struct {
 
 	healthCheckGroup *singleflight.Group[string, *healthcheck.Report]
 	healthCheckCache atomic.Pointer[healthcheck.Report]
+
+	statsBatcher *batchstats.Batcher
 }
 
 // Close waits for all WebSocket connections to drain before returning.