Add warning about case insensitive term queries in 2.x (opensearch-project#9170)

* Add warning about case insensitive term queries in 2.x

Signed-off-by: Daniel Widdis <[email protected]>

* Be more vague on performance impact

Signed-off-by: Daniel Widdis <[email protected]>

* Update _query-dsl/term/term.md

Signed-off-by: kolchfa-aws <[email protected]>

---------

Signed-off-by: Daniel Widdis <[email protected]>
Signed-off-by: kolchfa-aws <[email protected]>
Co-authored-by: kolchfa-aws <[email protected]>

Author: dbwiddis

_query-dsl/term/term.md

@@ -42,6 +42,9 @@ GET shakespeare/_search
 ```
 {% include copy-curl.html %}
 
+In OpenSearch 2.x and earlier, complexity can increase exponentially with the number of characters, leading to high heap memory usage and reduced performance. To avoid this, do not use case-insensitive searches. Instead, apply a [lowercase token filter]({{site.url}}{{site.baseurl}}/analyzers/token-filters/lowercase/) in the indexed field's analyzer and use lowercase query terms.
+{: .warning}
+
 The response contains the matching documents despite any differences in case:
 
 ```json