Add possibility to assign groups to newly added entries from the beginning

[DL6ER]

What does this implement/fix?

See the related Discourse Feature request for screenshots: https://discourse.pi-hole.net/t/add-group-management-dropdown-to-add-a-new-domain-or-regex-filter/74696

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Related issue or feature (if applicable): https://discourse.pi-hole.net/t/add-group-management-dropdown-to-add-a-new-domain-or-regex-filter/74696

Pull request in docs with documentation (if applicable): N/A

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