Implement new OIDC login for users

[SkylordA]

Currently uses username/password for password grant access via the access_token/ endpoint on the platform. This is done implicitly via the OasisLMF APIClient class.

When this issue (OasisLMF/OasisPlatform#1223) is finally merged, allowing generic OIDCs, the authorization method will be changed for users and will require redirecting to the OIDC login page via the new authorize/ endpoint. The tokens can then be retrieved in the UI and passed to APIClient directly in order to login.

This will be implemented already in OasisUI when generic OIDC is released.