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

plugins/sso/migrations/sqlite/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" integer NOT NULL DEFAULT 0;
+-- 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" = 1;