Use asab.web.auth middleware

[byewokko]

• This is a proposal to make authorization and access control more consistent across the ASAB ecosystem.
• SCA could adapt and extend the asab.web.auth middleware (https://github.com/TeskaLabs/asab/blob/master/asab/web/auth/service.py) instead of having its own fully independent implementation.
• SCA would override AuthService._authenticate_request method with its own internally handled authentication (without needind to communicate with an external auth server). Also the _fetch_public_keys_if_needed and is_ready methods would need to be overridden.
• Otherwise, the access control part of the AuthService including the decorators (https://github.com/TeskaLabs/asab/blob/master/asab/web/auth/decorator.py) should be transferrable without changes.
• This should easily work with the Admin container.
• Applicability to the Public container needs more investigation.