Add `/users/{id}` and `/clients/{id}` PATCH endpoints

[myssto]

Currently we are assigning users and clients their claims via direct database access. We need to implement endpoints to patch these via the API directly for use by admins.

We need to identify whether these should be delegated to their own controllers (UsersController and ClientsController), or if they could be reasonably integrated into a current controller (OAuthController).

Tasks:

• [x] Identify controller scheme for entities User and OAuthClient
• [x] PATCH endpoint for editing User.Scopes
• [ ] PATCH endpoint for editing OAuthClient.Scopes

[hburn7]

Using a proper UsersController would be appropriate here.