DOCS-13741 add warning to ttlMonitorEnabled param

Author: andf-mongodb

source/reference/parameters.txt

@@ -643,6 +643,8 @@ General Parameters
 
    |mongod-only|
 
+   *Default*: ``true``
+
    To support :doc:`TTL Indexes </core/index-ttl>`, :binary:`~bin.mongod`
    instances have a background thread that is responsible for deleting
    documents from collections with TTL indexes.
@@ -662,6 +664,13 @@ General Parameters
 
       mongod --setParameter ttlMonitorEnabled=false
 
+   .. important::
+
+      Do not run production :binary:`~bin.mongod` instances with
+      ``ttlMonitorEnabled`` disabled, except under guidance from MongoDB
+      support. Preventing TTL document removal can negatively impact
+      MongoDB internal system operations that depend on
+      :doc:`TTL Indexes </core/index-ttl>`.
 
 .. parameter:: disableJavaScriptJIT