DOCS-16200 $currentOp - targetAllNodes (#4724)

* DOCS-16200 Documents  targetAllNodes option

* Fixes build issue

* Fixes build issue

* Expands explanation of conditions

* Fixes build issue

* Fixes per Jeff

---------

Co-authored-by: Kenneth P. J. Dyer <kenneth.dyer@monodb.com>

Author: kennethdyer

source/reference/operator/aggregation/currentOp.txt

@@ -156,6 +156,24 @@ Syntax
        :binary:`~bin.mongod`.
 
        Defaults to ``false``.
+   * - :ref:`targetAllNodes <currentOp-stage-targetAllNodes>`
+
+     - .. _currentOp-stage-targetAllNodes:
+
+       Boolean.  If set to ``true``, ``$currentOp`` outputs a document 
+       for each data-bearing node for all shards.  If set to ``false``,
+       ``$curentOp`` outputs a document for each shard.
+
+       For example, in a sharded cluster with three shards where each shard
+       is a replica set with three nodes: 
+
+       - ``targetAllNodes=false`` outputs three documents
+
+       - ``targetAllNodes=true`` outputs nine documents
+
+       Defaults to ``false``.
+
+       .. versionadded:: 7.1
 
 Omitting any of the above parameters will cause $currentOp to use
 that parameter's default value. Specify an empty document, as shown