admin: move common sections to individual files

We don't specify ids for these sections and let docbook generate it
automatically.

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
admin/data-center: eliminate TODO of permission section

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
admin/storage-domain: eliminate TODO of permission section

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
admin/templates: eliminate TODO of permission section

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
admin/vm-disks: eliminate TODO of permission section

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
admin/vm: eliminate TODO of permission section

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>