Handle rate-limited 429 responses when testing integration settings

What does this MR do and why?

It:

• handles rate-limited 429 response with This endpoint has been requested too many times. Try again later. message.
• skips the Sentry notifications for the 429 error code

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Checkout the current branch
2. Navigate to one of integrations (e.g. http://localhost:3000/flightjs/Flight/-/settings/integrations/buildkite/edit)
3. Activate the integration and fill out the form
4. Click on the Test settings button more than 5 times
5. The new message should appear

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #365596 (closed)