Metadata field is not present in "Bounce" class

[robertop87]

Describe the bug Metadata field in Bounce response object is not present. It is very important for custom integrations, because it provides specific custom information for API consumers.

To Reproduce Provide steps to reproduce the behavior:

1. Open the Bounce.java
2. Verify that "metadata" field is not present

Expected behavior "metadata" field must be present, and it should be Map<String, String> or Map<String, Object>

Java (please complete the following information): No related to java

Additional context None