[DOCS] Add heading and anchor to reindex with ingest pipeline section (#64835) (#64894)

Co-authored-by: James Rodewig <40268737+jrodewig@users.noreply.github.com>

Co-authored-by: Mark Walkom <markw@elastic.co>

docs/reference/docs/reindex.asciidoc

@@ -410,6 +410,9 @@ POST _reindex
 --------------------------------------------------
 // TEST[s/^/PUT source\n/]
 
+[[reindex-with-an-ingest-pipeline]]
+===== Reindex with an ingest pipeline
+
 Reindex can also use the <<ingest>> feature by specifying a
 `pipeline` like this: