Add support for authentication with OIDC

[winston0410]

It would be great if Shiori would support single sign on using OIDC, and also support disabling registration with username and password completely. To implement this, I guess we will need the following env variables:

SHIORI_OIDC_BASE_URI=xxx
SHIORI_OIDC_CLIENT_ID=xxx
SHIORI_OIDC_CLIENT_SECRET=xxx

This will only support one OIDC provider. If we want to support multiple providers, allowing a configuration file would be ideal.

And then we map the sub claim from the JWT token we retrieve from OIDC provider to the user id used by Shiori right now.