Add OIDC section for sign in and sign up page

- name: :oidc → Identifier for this login provider in the app.
- scope: [:openid, :email, :profile] → Tells the provider we want the user’s ID (openid), their email, and basic profile info (name, picture, etc.).
- response_type: :code → Uses Authorization Code Flow, which is more secure because tokens are not exposed in the URL.
- issuer: Rails.application.secrets.oidc_issuer → The base URL of the OIDC provider (e.g., Auth0). Used to find its config.
- discovery: true → Automatically fetches the provider’s endpoints from its discovery document instead of manually setting them.
- client_auth_method: :basic → Sends client ID and secret using HTTP Basic Auth when exchanging the code for tokens.

Add system tests for OIDC Auth

Edit the oauth docs to support OIDC auth

app/components/devise/omniauth_form_component.rb

@@ -17,7 +17,8 @@ class Devise::OmniauthFormComponent < ApplicationComponent
         (:facebook if feature?(:facebook_login)),
         (:google_oauth2 if feature?(:google_login)),
         (:wordpress_oauth2 if feature?(:wordpress_login)),
-        (:saml if feature?(:saml_login))
+        (:saml if feature?(:saml_login)),
+        (:oidc if feature?(:oidc_login))
       ].compact
     end
 end