Add Guile internal time metrics

As this will help identify when the service restarts.

guix-data-service/web/controller.scm

@@ -173,6 +173,17 @@
          (gc-metrics-updater
           (get-gc-metrics-updater registry)))
 
+    (define guile-time-metrics-updater
+      (let ((internal-real-time
+             (make-gauge-metric registry "guile_internal_real_time"))
+            (internal-run-time
+             (make-gauge-metric registry "guile_internal_run_time")))
+        (lambda ()
+          (metric-set internal-real-time
+                      (get-internal-real-time))
+          (metric-set internal-run-time
+                      (get-internal-run-time)))))
+
     (lambda ()
       (letpar& ((metric-values
                  (with-thread-postgresql-connection
@@ -279,6 +290,7 @@
                   load-new-guix-revision-job-metrics)
 
         (gc-metrics-updater)
+        (guile-time-metrics-updater)
 
         (list (build-response
                #:code 200