Implements a client provider store for NCO usage

Context

Since NEV-41, we now have an oauth2 flow for authentication against ARender Previewer.
This mechanism gets its OAuth2 provider configuration from the ARender Previewer configuration engine (environment variables or properties).

Request

We want to implement the Spring Security interface ClientRegistrationRepository in order to get OAuth2 provider configuration from a datastore; This will allow us to configure several provider and thus connect ARender stack to several Nuxeo.

We need to have a mechanism to correctly configure this part. We'll do something similar to NEV-261. Our need here is to remove the classic provider configuration through properties or environment variables and declare the DB implementation in order to fetch providers configuration.

We also need to change Nuxeo ARender connector in order to give to ARender the OAuth2 client to use for authentication flow.