Add message id to fin_agent_replied_event schema

Add an id field to the message object in the fin_agent_replied_event schema
in versions 0 (Preview base), 2.14, and 2.15. This enables consumers to
deduplicate fin_replied events received via both SSE and webhooks.

Towards intercom/intercom#496283

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rahulgdsouza

descriptions/0/api.intercom.io.yaml

@@ -25466,6 +25466,10 @@ components:
           type: object
           description: Fin's answer to the user's query.
           properties:
+            id:
+              type: string
+              description: A unique identifier for this message.
+              example: '98765'
             author:
               type: string
               enum:

descriptions/2.14/api.intercom.io.yaml

@@ -19976,6 +19976,10 @@ components:
           type: object
           description: Fin's answer to the user's query.
           properties:
+            id:
+              type: string
+              description: A unique identifier for this message.
+              example: '98765'
             author:
               type: string
               enum:

descriptions/2.15/api.intercom.io.yaml

@@ -20804,6 +20804,10 @@ components:
           type: object
           description: Fin's answer to the user's query.
           properties:
+            id:
+              type: string
+              description: A unique identifier for this message.
+              example: '98765'
             author:
               type: string
               enum: