Allow option to keep the containers alive

It would be nice to keep the docker containers alive for speeding up the test runs. Now, in every test run containers are re-created and can't keep them alive since this block

  def __del__(self):
        """
        Try to remove the container in all circumstances
        """
        if self._container is not None:
            try:
                self.stop()
            except:  # noqa: E722
                pass

removes containers when the instance variable is deleted (when the program terminates) and I cannot override it because this also runs without using with as block.

I don't want my Mysql container to be recreated everytime. I am running tests very frequently and I am waiting couple seconds everytime. Pretty annoying.

I can make a small PR if that makes sense?

Comienza leyendo testcontainers/core/container.py alrededor del método del y sigue cómo se detienen los contenedores cuando termina una ejecución de pruebas, incluido el uso fuera de un bloque with. Define el comportamiento del ciclo de vida de la opción tanto para contenedores gestionados por contexto como para contenedores creados directamente; se considera terminado cuando un llamador puede mantener un contenedor MySQL activo entre ejecuciones sin limpieza automática.