feat: updated the DA input existing_cos_instance_crn to use resource picker widget (#1079)

Author: Khuzaima05

ibm_catalog.json

@@ -386,9 +386,19 @@
                 {
                   "type": "regex",
                   "description": "The value provided for 'existing_cos_instance_crn' is not valid.",
-                  "value": "^crn:(.*:){3}cloud-object-storage:(.*:){2}[0-9a-fA-F]{8}(?:-[0-9a-fA-F]{4}){3}-[0-9a-fA-F]{12}::$"
+                  "value": "^__NULL__$|^crn:(.*:){3}cloud-object-storage:(.*:){2}[0-9a-fA-F]{8}(?:-[0-9a-fA-F]{4}){3}-[0-9a-fA-F]{12}::$"
                 }
-              ]
+              ],
+              "custom_config": {
+                "type": "platform_resource",
+                "grouping": "deployment",
+                "original_grouping": "deployment",
+                "config_constraints": {
+                  "resourceType": "cloud-object-storage",
+                  "selection": "single_select",
+                  "valueType": "crn"
+                }
+              }
             },
             {
               "key": "skip_vpc_cos_iam_auth_policy"