fix: updated the DA default version to be 8.15 (#533)

Author: jor2

ibm_catalog.json

@@ -206,6 +206,7 @@
             {
               "key": "elasticsearch_version",
               "required": true,
+              "default_value": "8.15",
               "options": [
                 {
                   "displayname": "8.15",
@@ -652,6 +653,7 @@
             {
               "key": "elasticsearch_version",
               "required": true,
+              "default_value": "8.15",
               "options": [
                 {
                   "displayname": "8.15",