User details page (#26713)

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>


![grafik](1ad57ac9-f20a-45a4-8477-ffe572a41e9e)


![grafik](25786ecd-cb9d-4c92-90f4-e7f4292c073b)


</details>

Partially resolves #25939

---------

Co-authored-by: Giteabot <teabot@gitea.io>

options/locale/locale_en-US.ini

@@ -2823,6 +2823,7 @@ users.list_status_filter.is_prohibit_login = Prohibit Login
 users.list_status_filter.not_prohibit_login = Allow Login
 users.list_status_filter.is_2fa_enabled = 2FA Enabled
 users.list_status_filter.not_2fa_enabled = 2FA Disabled
+users.details = User Details
 
 emails.email_manage_panel = User Email Management
 emails.primary = Primary