Issue Summary

When navigating to connect JCMA/CCMA to a cloud site using "Choose cloud site", if the user is added to many cloud sites the  
POST https://migration-service.services.atlassian.com/gateway/api/permissions/permitted API may return 429 due to rate limiting. This causes the page to fail to load and blocks migration. 

Steps to Reproduce

1. Navigate to the "Choose cloud site" option when creating a migration plan in JCMA
   
2. Observe that the page does not load correctly and shows "Failed to load destination sites data"
   

Expected Results

The page correctly loads allowing the user to select which cloud site they wish to migrate to.

Actual Results

Using the browser network tab, one or more calls to the POST https://migration-service.services.atlassian.com/gateway/api/permissions/permitted API returns HTTP status code 429 with the following response JSON:

{
  "code": 429,
  "message": "Request has been rate limited"
} 

Workaround

Currently the only work around known for this behaviour is to attempt to connect to a cloud site using a different user. By using a user that can access fewer cloud sites there is less chance of the permitted API being rate limited.