feat(external users): email sanity + mock SMTP

- SMTP has a mock to enable end to end test and validate the whole path
     (via OXICLOUD_SMTP_MOCK)
    - add email normalisation ( including punicode)
    - api to share to external user

src/infrastructure/services/mod.rs

@@ -14,6 +14,7 @@ pub mod local_blob_backend;
 pub mod login_lockout_service;
 pub mod migration_blob_backend;
 pub mod migration_job;
+pub mod mock_email_sender;
 pub mod nextcloud_chunked_upload_service;
 pub mod oidc_service;
 pub mod password_hasher;