[DOCS] Linked cat-pending to cluster-pending

docs/reference/cat/pending_tasks.asciidoc

@@ -2,7 +2,8 @@
 == Cluster Pending Tasks
 
 `pending_tasks` provides the same information as the
-`/_cluster/pending_tasks` API in a convenient tabular format.
+<<cluster-pending,`/_cluster/pending_tasks`>> API in a
+convenient tabular format.
 
 [source,shell]
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