Add data-streams-mappings to isXPackTemplate method (elastic#73633)

This template was added in elastic#64978, however, there can be some test failures if we try to remove
built-in templates. It was missing from the list and now needs to be added back.

Author: dakrone

test/framework/src/main/java/org/elasticsearch/test/rest/ESRestTestCase.java

@@ -1583,6 +1583,7 @@ protected static boolean isXPackTemplate(String name) {
             case "ilm-history":
             case "logstash-index-template":
             case "security-index-template":
+            case "data-streams-mappings":
                 return true;
             default:
                 return false;