DOCS-14251 add opportunisticSecondaryTargeting v4.2 only

Author: andf-mongodb

source/reference/parameters.txt

@@ -2615,6 +2615,42 @@ Sharding Parameters
 
    - MongoDB 3.4.11+
 
+.. parameter:: opportunisticSecondaryTargeting
+
+   .. versionadded:: 4.2.13
+
+   |mongos-only|
+
+   Type: boolean
+
+   Default: false
+
+   When ``true``, enables a :binary:`~bin.mongos` to attempt to
+   establish connections to multiple secondaries and direct the request 
+   to the first secondary that accepts the connection.
+
+   .. note::
+
+      This feature was introduced in MongoDB 4.2.0 and enabled
+      by default. Starting in MongoDB 4.2.13, this feature is now
+      disabled by default. The
+      :parameter:`opportunisticSecondaryTargeting` parameter is
+      introduced alongside this change to permit re-enabling this
+      feature if desired.
+
+   The following enables :parameter:`opportunisticSecondaryTargeting`:
+
+   .. code-block:: sh
+
+      mongos --setParameter opportunisticSecondaryTargeting=true
+
+   The parameter may also be set using the :dbcommand:`setParameter`
+   command:
+
+   .. code-block:: javascript
+
+      db.adminCommand( { setParameter: 1, opportunisticSecondaryTargeting: true } )
+
 Storage Parameters
 ~~~~~~~~~~~~~~~~~~