Add source to the ChartUnfurlRequest to accompany the unfurlId as an alternative means of specifying the destination of the unfurl (#843)

Author: ribsalad

slack-api-client/src/main/java/com/slack/api/methods/RequestFormBuilder.java

@@ -1206,6 +1206,7 @@ public static FormBody.Builder toForm(ChatUnfurlRequest req) {
         setIfNotNull("user_auth_blocks", req.getUserAuthBlocks(), form);
         setIfNotNull("user_auth_url", req.getUserAuthUrl(), form);
         setIfNotNull("unfurl_id", req.getUnfurlId(), form);
+        setIfNotNull("source", req.getSource(), form);
         return form;
     }
 

slack-api-client/src/main/java/com/slack/api/methods/request/chat/ChatUnfurlRequest.java

@@ -65,6 +65,9 @@ public class ChatUnfurlRequest implements SlackApiRequest {
     // https://api.slack.com/changelog/2021-08-changes-to-unfurls
     private String unfurlId;
 
+    // https://api.slack.com/changelog/2021-08-changes-to-unfurls
+    private String source;
+
     // https://api.slack.com/docs/message-link-unfurling#unfurls_parameter
     @Data
     public static class UnfurlDetail {