chore: add pacemaker

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/internal/csm/Pacemaker.java

@@ -30,7 +30,7 @@ class Pacemaker implements Runnable {
 
   private Instant prev;
 
-  Pacemaker(RecorderRegistry registry, ClientInfo clientInfo, String name) {
+  public Pacemaker(RecorderRegistry registry, ClientInfo clientInfo, String name) {
     this.prev = Instant.now();
     this.registry = registry;
     this.clientInfo = clientInfo;