[FEAT] Admin user role

[NeonDaniel]

Objective

Currently, all users have the same level of access and any administrative tasks are expected to be done via manual configuration changes. Adding the concept of an "admin" user would allow for exposing more configuration options via Web UIs and simplify tasks like endpoint configuration, persona creation, etc.

Initial Implementation Requirements

• Define updates to the user database schema to identify "admin" users
• Define a default admin account, or YAML configuration option to define "super admin" or first "admin" user
• Define an admin management page where admin users (or the "super admin") can mark other accounts as "admin"

Other Considerations

• Administrative tasks will need to be defined and implemented independent of this issue (i.e. configuration/persona management)
• Possibly related to [FEAT] Google Oauth support #39