Rate limit the integration testing feature

What does this MR do and why?

What

This adds rate limits for the integration testing feature, preventing the abuse of the test functionality.

Screenshots or screen recordings

Before

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Checkout the 356149-rate-limit-the-integration-testing-endpoint-2 branch and run the app locally
2. Visit the integration page of one project and choose one (e.g. MicrosoftTeams notification)
3. Fill out the form and click on the Test settings button more than 5 times
4. 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 #356149 (closed)