Show import history to instance Admins
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### Problem
With https://gitlab.com/groups/gitlab-org/-/epics/17359+ the import results for a top-level group are visible to all Owners of that group and Admin, if they navigate to the group page.
However, Admin doesn't have an overview of all imports that have happened on the instance.
### Proposed solution
Show import history page in the Admin UI, that would include all imports done to an instance.

Figma link -> https://www.figma.com/design/c67Fu98Fxcrn7uTR234GXm/Import-and-Integrate-follow-ups-from-17.9?node-id=1-94&t=okoHIOWCznpLubO9-1
Table component -> https://gitlab.com/gitlab-org/gitlab/-/merge_requests/180098
#### Emails
With https://gitlab.com/groups/gitlab-org/-/epics/17359+ all the group Owners will be notified by email about the import to a group they own. SM and Dedicated Admin might want to be notified as well, while .com Admins might not want tot be notified on each import.
Could we add an Admin setting to opt-in to receive emails upon completed imports? By default it would be off, to keep the current behaviour.
issue