default This registerColumnMapper(Type type, ColumnMapper<?> mapper) {
        return configure(ColumnMappers.class, c -> c.register(type, mapper));
    }
Convenience method for {@code getConfig(ColumnMappers.class).register(type, mapper)}

@param type   the type to register
@param mapper the mapper to use on that type
@return this
core/src/main/java/org/jdbi/v3/core/config/Configurable.java