feat: Enrich super admin and admin role by assigning their respective roles

[Lanhild]

There's been a new super admin role since the 0.1.123 version to restrict user actions to other admins.

It'd be useful if model downloading/deletion were restricted to the super admin.

[Lanhild]

After being confused by the 2nd line;

User action buttons from the admin panel are now disabled for users with admin roles.

I discussed with another contributor about this, and thought some modifications would be necessary for this new "super admin" role

• Make the super admin role assignable by other super admins
• Super admin should be the only one able to see others chats, modify roles or modify users
• "Normal" admins would preserve their current permissions, minus the latter

Below is a transcript of our conversation.

[Lanhild]

@tjbck here's a link to a table describing the needs/permissions for this "Super Admin" role.

It restricts "Admin" permissions a lot, but it makes sense in the way that the "Super Admin"(s) exists, and mitigates the risk of a bad actor compromising one's WebUI instance.

https://docs.google.com/spreadsheets/d/1Zb6_aC3h-wPb7K7eVxFYO9PV0k4PAlIUKM0AxRQd_dc/edit?usp=sharing

Anyhow, once we have the role for that, it'll be easier in the future to allow/restrict other features.