[API] change wait_for_completion defaults according to docs (#23672)

rest-api-spec/src/main/resources/rest-api-spec/api/delete_by_query.json

@@ -146,7 +146,7 @@
         },
         "wait_for_completion": {
            "type" : "boolean",
-           "default": false,
+           "default": true,
            "description" : "Should the request should block until the delete-by-query is complete."
         },
         "requests_per_second": {

rest-api-spec/src/main/resources/rest-api-spec/api/reindex.json

@@ -22,7 +22,7 @@
         },
         "wait_for_completion": {
           "type" : "boolean",
-          "default": false,
+          "default": true,
           "description" : "Should the request should block until the reindex is complete."
         },
         "requests_per_second": {

rest-api-spec/src/main/resources/rest-api-spec/api/update_by_query.json

@@ -154,7 +154,7 @@
         },
         "wait_for_completion": {
            "type" : "boolean",
-           "default": false,
+           "default": true,
            "description" : "Should the request should block until the update by query operation is complete."
         },
         "requests_per_second": {