Disable replication lag tracking by configuration

Introduce the new configuration settings
ref-database.replicationLagEnabled for disabling the metric to trace
the auto-replication lag between sites.

The rationale for disabling this metric lies in the use of
mono-repos with very frequent updates which would cause the ref
refs/multi-site/version/* to be continuously updated causing
packed-refs locks and consuming precious resources on the
global-refdb.

When using pull-replication and apply-object, the value of using the
refs/multi-site/version/* for tracking is not very useful anyway
because it gets replicated outside the batch.

Bug: Issue 313856493
Change-Id: I6b32e0423ed894793f55ed57c60cc356ebe2a31a

src/main/resources/Documentation/config.md

diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index 0485d5b..7547fd9 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -95,10 +95,18 @@
 :   Enable the use of a shared ref-database
     Defaults: true
 
+```ref-database.replicationLagEnabled```
+:   Enable the metrics to trace the auto-replication lag between sites
+    updating the `refs/multi-site/version/*` to the _epoch_ timestamp in
+    milliseconds. Please note that the `replication-lag` REST-API is also
+    disabled if this setting is false.
+    Defaults: true
+
 ```ref-database.replicationLagRefreshInterval```
 :   Enable the auto-refresh of the metrics to trace the auto-replication
     lag by polling on a regular basis. Set to zero for disabling the polling
-    mechanism.
+    mechanism. Disabled automatically when `ref-database.replicationLagEnable`
+    is set to false.
     Defaults: 60 min
 
 ```ref-database.enforcementRules.<policy>```