Add new errorCode 4 of NarrowcastProgressResponse (#1519)

A new errorCode has been added to NarrowcastProgressResponse.
New number is 4. 4 means an audience of less than 50 recipients is
included as a condition of sending.

Previously, it was not possible to determine whether an error occurred
due to a lack of enough recipients or because an audience of less than
50 recipients is included as a condition of sending. This will be fixed
with the update to the Messaging API, so the description of errorCode on
OpenAPI will also be revised.

Co-authored-by: github-actions <github-actions@github.com>

Author: github-actions[bot]

clients/line-bot-messaging-api-client/src/main/java/com/linecorp/bot/messaging/model/NarrowcastProgressResponse.java

@@ -61,7 +61,8 @@ public record NarrowcastProgressResponse(
      * Error summary. This is only included with a phase property value of failed. One of:
      * `1`: An internal error occurred. `2`: An error occurred because there
      * weren't enough recipients. `3`: A conflict error of requests occurs because a
-     * request that has already been accepted is retried.
+     * request that has already been accepted is retried. `4`: An audience of less than 50
+     * recipients is included as a condition of sending.
      */
     @JsonProperty("errorCode") Long errorCode,
     /**