Add OAuth authentication

[IgnisDa]

• Fixes [Feature Request] Oauth / OpenID #522.
• Fixes RelativeUrlWithoutBase error due to double quotes in db url #753.

[IgnisDa]

• Make a backup of your database using the guide.
• Setup OpenID on your instance using the guide.
• Logout of your original account and then click on "Continue with OpenID Connect". Continue with user you want to select, after which a new account will be created. Let's say that I want IgnisDa below to be able to login using OIDC (of ignisda2001@gmail.com):
  
• Drop into your database (docker exec -u postgres -it ryot-db psql) and copy the oidc_issuer_id of the new user and then delete it using DELETE FROM "user" WHERE id = 6;
• Update details of the old user using UPDATE "user" SET oidc_issuer_id = '104798859970005336426', password = NULL WHERE id = 1;. After this, it should look like this:
  

You should now be able login using OIDC. The same procedure needs to be followed for all users that want their provider changed to OIDC.