Support worker shared memory declaration

Depends https://gitlab.com/teklia/arkindex/ponos/-/issues/129

The workers need to be able to report a specific value for shm_size in their own configuration (no user configuration support, it's only setup by the developer of the training code for now).

Format to support :

The format is . number must be greater than 0. Unit is optional and can be b (bytes), k (kilobytes), m (megabytes), or g (gigabytes)

The value will be set under docker.shm_size parameter in the worker YAML configuration (please make a MR for the documentation website too).