feat: move sso and ldap logins into plugins (C2)

plugins/sso/migrations/mysql/0002_legacy_callback.sql

@@ -0,0 +1,7 @@
+-- sso 0002: legacy_callback
+-- Generated by termix-plugin migrations. Review before committing.
+
+ALTER TABLE `p_sso_providers` ADD COLUMN `legacy_callback` boolean NOT NULL DEFAULT false;
+-- Providers that existed before 2.9 were registered with the identity
+-- provider under /users/oidc/callback, so they keep sending that URI.
+UPDATE `p_sso_providers` SET `legacy_callback` = true;