feat: add e2e workspace build duration metric (#21739)

Adds coderd_template_workspace_build_duration_seconds histogram that
tracks the full duration from workspace build creation to agent ready.
This captures the complete user-perceived build time including
provisioning and agent startup.

The metric is emitted when the agent reports ready/error/timeout via the
lifecycle API, ensuring each build is counted exactly once per replica.

coderd/agentapi/api.go

@@ -89,6 +89,7 @@ type Options struct {
 	PublishWorkspaceAgentLogsUpdateFn func(ctx context.Context, workspaceAgentID uuid.UUID, msg agentsdk.LogsNotifyMessage)
 	NetworkTelemetryHandler           func(batch []*tailnetproto.TelemetryEvent)
 	BoundaryUsageTracker              *boundaryusage.Tracker
+	LifecycleMetrics                  *LifecycleMetrics
 
 	AccessURL                 *url.URL
 	AppHostname               string
@@ -170,6 +171,7 @@ func New(opts Options, workspace database.Workspace) *API {
 		Database:                 opts.Database,
 		Log:                      opts.Log,
 		PublishWorkspaceUpdateFn: api.publishWorkspaceUpdate,
+		Metrics:                  opts.LifecycleMetrics,
 	}
 
 	api.AppsAPI = &AppsAPI{