Adds the CE backport for EE!11226

What does this MR do?

This is the CE backport for https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/11226

It excludes buttons inside groups from inheriting the margin that is applied to all the buttons in the modal footers.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• [-] Code review guidelines
• [-] Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• Separation of EE specific content

Performance and testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers