Add team_assignment_limit_change activity type to OpenAPI spec

Adds OpenAPI documentation for team assignment limit changes in activity logs API.

Changes:
- Adds team_assignment_limit_change to activity_type enum in both Unstable (0) and Stable (2.14)
- Adds team (object with id and name) metadata field
- Adds team_assignment_limit (nullable integer) metadata field

The metadata structure follows the pattern of conversation_assignment_limit and ticket_assignment_limit,
storing only the current value rather than both old and new values.

This is an additive, non-breaking change suitable for the stable version.

Related PRs:
- intercom/intercom#446612 (Updated API presenter implementation)
- intercom/intercom#445742 (Initial API presenter implementation)
- intercom/intercom#445704 (Event infrastructure)

Related Issue: intercom/intercom#445916

Follows pattern from PR #293 (admin assignment limits).

Author: salmanbshah

descriptions/0/api.intercom.io.yaml

@@ -15109,6 +15109,7 @@ components:
           - app_team_creation
           - app_team_deletion
           - app_team_membership_modification
+          - team_assignment_limit_change
           - app_timezone_change
           - app_webhook_creation
           - app_webhook_deletion
@@ -15230,6 +15231,24 @@ components:
           nullable: true
           description: The ticket assignment limit value for an admin.
           example: 20
+        team:
+          type: object
+          nullable: true
+          description: Details about the team whose assignment limit was changed.
+          properties:
+            id:
+              type: integer
+              description: The ID of the team.
+              example: 123
+            name:
+              type: string
+              description: The name of the team.
+              example: Support Team
+        team_assignment_limit:
+          type: integer
+          nullable: true
+          description: The team assignment limit value (null if limit was removed).
+          example: 50
     addressable_list:
       title: Addressable List
       type: object

descriptions/2.14/api.intercom.io.yaml

@@ -14072,6 +14072,7 @@ components:
           - app_team_creation
           - app_team_deletion
           - app_team_membership_modification
+          - team_assignment_limit_change
           - app_timezone_change
           - app_webhook_creation
           - app_webhook_deletion
@@ -14193,6 +14194,24 @@ components:
           nullable: true
           description: The ticket assignment limit value for an admin.
           example: 20
+        team:
+          type: object
+          nullable: true
+          description: Details about the team whose assignment limit was changed.
+          properties:
+            id:
+              type: integer
+              description: The ID of the team.
+              example: 123
+            name:
+              type: string
+              description: The name of the team.
+              example: Support Team
+        team_assignment_limit:
+          type: integer
+          nullable: true
+          description: The team assignment limit value (null if limit was removed).
+          example: 50
     addressable_list:
       title: Addressable List
       type: object