fix(integration): Fix rate limit handling (#2686)

## Context

This PR follows #2570

## Description

It updates the way we check for the presence of the rate error limit
code in the payload to avoid parsing the JSON body and be independent
from the format of the response.

app/services/integrations/aggregator/base_service.rb

@@ -123,9 +123,7 @@ def message(error)
       def request_limit_error?(http_error)
         return false unless http_error.error_code.to_i == 500
 
-        http_error.json_message.dig('error', 'payload', 'error', 'code') == REQUEST_LIMIT_ERROR_CODE
-      rescue JSON::ParserError
-        false
+        http_error.error_body.include?(REQUEST_LIMIT_ERROR_CODE)
       end
     end
   end