Clarify ignore_above behavior with arrays of strings

Currently docs don't explain how `ignore_above` behaves with arrays of
strings.

Clarify how `ignore_above` applies for arrays of strings and
also note that all string(s) will still be visible in the
`_source` field.

Relates #33057

docs/reference/mapping/params/ignore-above.asciidoc

@@ -2,6 +2,9 @@
 === `ignore_above`
 
 Strings longer than the `ignore_above` setting will not be indexed or stored.
+For arrays of strings, `ignore_above` will be applied for each array element separately and string elements longer than `ignore_above` will not be indexed or stored.
+
+NOTE: All strings/array elements will still be present in the `_source` field, if the latter is enabled which is the default in Elasticsearch.
 
 [source,js]
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