Update conversation webhook field descriptions for v2.15+ plain text serialization (#373)

Note that body and subject fields in conversation webhook payloads return plain text instead of HTML in API version 2.15+.

Co-authored-by: lauraintercom <laura.owens@intercom.io>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

descriptions/2.15/api.intercom.io.yaml

@@ -17543,7 +17543,8 @@ components:
           type: string
           nullable: true
           description: The message body, which may contain HTML. For Twitter, this
-            will show a generic message regarding why the body is obscured.
+            will show a generic message regarding why the body is obscured. In webhook
+            payloads for API version 2.15+, this field returns plain text.
           example: "<p>Okay!</p>"
         created_at:
           type: integer
@@ -17775,12 +17776,14 @@ components:
         subject:
           type: string
           description: Optional. The message subject. For Twitter, this will show
-            a generic message regarding why the subject is obscured.
+            a generic message regarding why the subject is obscured. In webhook
+            payloads for API version 2.15+, this field returns plain text.
           example: ''
         body:
           type: string
           description: The message body, which may contain HTML. For Twitter, this
-            will show a generic message regarding why the body is obscured.
+            will show a generic message regarding why the body is obscured. In webhook
+            payloads for API version 2.15+, this field returns plain text.
           example: "<p>Hey there!</p>"
         author:
           "$ref": "#/components/schemas/conversation_part_author"