Use comma-separated IDs for skipping groups

What does this MR do and why?

Previously, skip_groups passed IDs using array notation which created long URLs (e.g., skip_groups%5B%5D=1&skip_groups%5B%5D=2). With 50+ groups in the GitLab for Jira Cloud app, this would exceed NGINX's header buffer size causing 502 errors.

Changed to use comma-separated format (skip_groups=1%2C2) to reduce URL length. This maintains API compatibility via ::API::Validations::Types::CommaSeparatedToIntegerArray and increases the limit to ~800 groups as a temporary solution.

References

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• #513621 (closed)

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Before	After

video2040248769

How to set up and validate locally

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

1. Set up Gitpod and ensure it is publicly accessible.
2. Install the GitLab for Jira Cloud app manually into a Jira Cloud account.
3. Configure the GitLab for Jira Cloud app
   • Link 3 groups and refresh the page
   • When you try and link more groups, you will notice that the API call to /api/v4/groups is much shorter as skip_groups is passing a comma-separated string rather than skip_groups[].