Frontend: Use DLP as OpenID Connect Provider

[rreitmann]

• check sso before app bootstrapping
• remove adminstration/usermanagement
• auth service needs to become the wrapper around the openid client, principal needs to use it
• redirects from/to login page need to be reworked
• welcome dialog handling must use DLP User API (=> DLP User APi must offer save)
• authenticated users must be able to order data packages (landing pages must be shown regardless of being authenticated or not)
• adjust robot framework tests
• projectmanagement: query users by login and email and role, and assign to project group (exlude already assigned ones)

[rreitmann]

There is a Pull Request for this feature: https://github.com/dzhw/metadatamanagement/pull/3037

The following topics are open:

• welcome dialog handling (identity provider currently does not return this claim in the id token)
• testing on the dev-system and on the test-system
• adjust E2E-tests
• user migration (dev, test -> DLP stage, prod -> DLP prod)
• buildconfiguration (setup environment variables for the client build e.g. CLIENT_ID_DEV, CLIENT_ID_TEST, ...)
• second browser tab handling needs to be improved