SLM PUT: add precision on date math support in indices parameter (#55203)

It was not clear for me that `indices` parameter supports date math expression.

I think it may be worth to add the precision in the documentation.

docs/reference/slm/apis/slm-put.asciidoc

@@ -67,7 +67,8 @@ If `true`, cluster states are included in snapshots. Defaults to `false`.
 
 `indices`::
 (Optional, array of strings)
-Array of index names or wildcard pattern of index names included in snapshots.
+Array of index names or wildcard pattern of index names included in snapshots. It
+supports <<date-math-index-names,date math>> expressions.
 ====
 
 `name`::