Release 3.0.0

[senid231]

Bumps the version to 3.0.0. Merge after #24.

Major because three changes can break a working host.

Upgrade notes

• Ruby 3.3 or later is required. The 3.2 floor is gone (Drop EOL Ruby and Rails from CI #22).
• Configuration::DEFAULT_LOGIN_PATH and DEFAULT_LOGOUT_PATH are removed. Read ActiveAdmin::Oidc.config.login_path and logout_path instead (Derive every mounted path from ActiveAdmin's namespace #17).
• Hosts whose ActiveAdmin namespace is not :admin: the login, logout and OmniAuth paths now follow the namespace. With default_namespace = :backoffice, the callback moves from /admin/auth/oidc/callback to /backoffice/auth/oidc/callback. Register the new callback URL with your identity provider, and update c.redirect_uri if you set it. To keep the old URLs, set c.login_path, c.logout_path and c.omniauth_path_prefix to the /admin values (Derive every mounted path from ActiveAdmin's namespace #17, Follow a host-set Devise.omniauth_path_prefix in the strategy too #21).

Hosts on the default :admin namespace need no changes.

Fixes

• Sign-in works when devise.rb sets omniauth_path_prefix (Follow a host-set Devise.omniauth_path_prefix in the strategy too #21).
• Namespaces such as :"admin-panel" route to /admin_panel, as ActiveAdmin does (Follow a host-set Devise.omniauth_path_prefix in the strategy too #21).
• require "activeadmin-oidc" no longer raises on Rails 8.1 (Fix NoMethodError on Rails 8.1 and move the ActiveAdmin 4.0 leg to it #23).
• New omniauth_route_prefix option for engine-mounted Devise (Derive every mounted path from ActiveAdmin's namespace #17).