fix(examples): fix access control model for Users.

[rikrose]

In the multi-tenant example, the access control model is broken - a tenant-admin could create, edit and delete super-admins, and make other users and themselves in to super-admins. This contribution fixes it so that:

• Only super-admins can create/edit/delete super-admins.
• Restrict tenant-admins from activities outside tenants they are admins for. Have not verified that this stops tenant-admins from editing users outside of their own tenants.
• Removes the button to Create/Delete in the admin console if the user is not a super-admin or tenant-admin.

Link to discussion on Discord: https://discord.com/channels/967097582721572934/1319199782996283443

[rikrose]

Basically the same logic in both changed files, which are only for access control to the Users collection in the multi-tenant example.

[rikrose]

Fixing formatting, per suggestion on Discord. Also took the opportunity to the same logic phrased the same way in both files.