Feature request: OpenID Connect authentication

[renne]

Paperless-ngx supports OpenID-Connect authentication.
In conjunction with the Nextcloud plugin OIDC Identity Provider the setup is quite simple:

1. Install and enable Nextcloud plugin OIDC Identity Provider
2. Add new OpenID Connect-Client in https://nextcloud.example.com/settings/admin/security
   1. Name = Paperless-ngx
   2. Redirect-URI = https://paperless.example.com
   3. Copy ClientID and secret
3. In the Paperless-ngx docker-compose.yml add environmnet variables for service webservice:

PAPERLESS_APPS: "allauth.socialaccount.providers.openid_connect"
PAPERLESS_SOCIALACCOUNT_PROVIDERS: '{"openid_connect": {"APPS": [{"provider_id": "nextcloud","name": "Nextcloud","client_id": "<Nextcloud client ID>","secret": "<Nextcloud client secret>","settings": { "server_url": "https://nextcloud.example.com"}}]}}'
PAPERLESS_DISABLE_REGULAR_LOGIN: true