This PR implements a proposal to clean up the admin users table by moving some information out to a separate user details page (which also displays some additional information). Other changes: - move edit user page from `/admin/users/{id}` to `/admin/users/{id}/edit` -> `/admin/users/{id}` now shows the user details page - show if user is instance administrator as a label instead of a separate column - separate explore users template into a page- and a shared one, to make it possible to use it on the user details page - fix issue where there was no margin between alert message and following content on admin pages <details> <summary>Screenshots</summary>   </details> Partially resolves #25939 --------- Co-authored-by: Giteabot <teabot@gitea.io>