Add OpenID Connect login support (#77)

* Add OpenID Connect login support
* Add docs for OIDC config with Google Auth
* Use Google styles for log in
- Add support for linking existing account
- Force users to sign-in with passoword first, when linking existing accounts
- Add support to create new user when using OIDC
- Add identities to user to prevent account take-ver
- Make tests mocking instead of being integration tests
- Manage session handling correctly
- use OmniAuth.config.mock_auth instead of passing auth data via request env
* Conditionally render Oauth button

- Set a config item `configuration.x.auth.oidc_enabled`
- Hide button if disabled

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Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>
Signed-off-by: soky srm <sokysrm@gmail.com>
Co-authored-by: sokie <sokysrm@gmail.com>

.env.test.example

@@ -1,5 +1,11 @@
 SELF_HOSTED=false
 
+# OpenID Connect for tests
+OIDC_ISSUER=
+OIDC_CLIENT_ID=
+OIDC_CLIENT_SECRET=
+OIDC_REDIRECT_URI=http://localhost:3000/auth/openid_connect/callback
+
 # ================
 # Data Providers
 # ---------------------------------------------------------------------------------