docs: add perl pod documentation to methods in `User.pm` (#6984)
docs: add perl pod documentation to methods in `User.pm` (#6984)

doc: add documentation
openfoodfacts/openfoodfacts-server,openfoodfacts/openfoodfacts-server,openfoodfacts/openfoodfacts-server,openfoodfacts/openfoodfacts-server,openfoodfacts/openfoodfacts-server