Description

Update this branch #389 to be compatible with CMS 5.

I have rebase code original branch feature/support-external-embargo-module with silverstripe-advancedworkflow -V6 for making it compatible with CMS 5.

Pull request checklist

• The target branch is correct
  • See picking the right version
• All commits are relevant to the purpose of the PR (e.g. no debug statements, unrelated refactoring, or arbitrary linting)
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• The commit messages follow our commit message guidelines
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• Code changes follow our coding conventions
• This change is covered with tests (or tests aren't necessary for this change)
• Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• CI is green