Include isAdmin when getting user as global/tenant admin

The following properties are present on the `/api/me` feed:

```
"isGlobalAdmin": true/false,
"isTenantAdmin": true/false,
```

However, when getting a user, these properties are currently not present. We should add these properties when a user is requested by a global admin. We should also add them when a user from Tenant X is requested by a tenant admin from Tenant X (but not Tenant Y).

This will then be used in the Admin UI to show if a user is a tenant admin or not and to show the appropriate action button.