Add support for Metadata#284

ajay-k merged 2 commits intomainnylas/nylas-java:mainfrom

bug-CUST-4508-v-3-java-sdk-missing-metadata-field-in-additional-field-typenylas/nylas-java:bug-CUST-4508-v-3-java-sdk-missing-metadata-field-in-additional-field-typeCopy head branch name to clipboard