Align `Cell` model with the catalogue

In the catalogue, we tweaked a couple of things about the cell model (see implementation and sample serialization).

@skoulouzis, does it make sense to modify the model used in the containerizer service to match the one in the catalogue?

If we keep the current model in the containerizer service, we will need to translate the cell representation to match the catalogue's model in the frontend (after receiving the response from NaaVRE-containerizer-service/containerize and posting the cell to NaaVRE-catalogue-service/workflow-cells/). This is doable, but we might create confusion by having two formulations of the cell model across different services.

Notable changes:

types is removed and its values merged with inputs, outputs, params or secrets. Eg.

{
  ...
  "inputs": [
    "test_input"
  ],
  "types": {
    "test_input": "float"
  },
}

becomes

{
  ...
  "inputs": [
    {
      "name": "test_input",
      "type": "float"
    }
  ]
}

param_values is removed and its values merged with params. Eg.

{
  ...
  "params": [
    "param_test"
  ],
  "types": {
    "param_test": "str"
  },
  "param_values": {
    "param_test": "foo"
}

becomes

{
  ...
  "params": [
    {
      "name": "param_test",
      "type": "str",
      "default_value": "\"foo\""
    }
  ],
}

renamed: base_image → base_container_image
added: description,virtual_lab(probably should be added in the frontend),container_imageandsource_url` (the source folder on GitHub)
removed: node_id, task_name, all_inputs, base_image, notebook_dict and original_source are removed
chart_obj is not in the catalogue model, but it would be nice to still return it for now. We don't have TS code to generate it in the frontend, but we have the Py code to generate it in the backend.
(owner, created, modified are automatically added upon creation in the catalogue)

NaaVRE / NaaVRE-containerizer-service

Align `Cell` model with the catalogue #10