Update Admin Activity Logs API with granular assignment limit types

This change introduces granular activity types for admin assignment limit changes,
allowing developers to distinguish between conversation and ticket assignment limits.

Changes:
- Split `admin_assignment_limit_change` into two separate activity types:
  - `admin_conversation_assignment_limit_change`
  - `admin_ticket_assignment_limit_change`
- Added new metadata fields to activity_log_metadata:
  - `conversation_assignment_limit`
  - `ticket_assignment_limit`

This is a follow-up to intercom/developer-docs#597

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: marcmlc

descriptions/0/api.intercom.io.yaml

@@ -14318,7 +14318,8 @@ components:
         activity_type:
           type: string
           enum:
-          - admin_assignment_limit_change
+          - admin_conversation_assignment_limit_change
+          - admin_ticket_assignment_limit_change
           - admin_away_mode_change
           - admin_deletion
           - admin_deprovisioned
@@ -14461,6 +14462,16 @@ components:
           nullable: true
           description: The name of the Admin who initiated the activity.
           example: Joe Example
+        conversation_assignment_limit:
+          type: integer
+          nullable: true
+          description: The conversation assignment limit value for an admin.
+          example: 15
+        ticket_assignment_limit:
+          type: integer
+          nullable: true
+          description: The ticket assignment limit value for an admin.
+          example: 20
     addressable_list:
       title: Addressable List
       type: object