Add jsonable abstract class or decorators for easy json encoding

[xgui3783]

To consider also: avoid circular references

[xgui3783]

from the discussion with @dickscheid , we have made the following way forward:

• a prototype refactor of siibra-python will be attempted, on https://github.com/FZJ-INM1-BDA/siibra-python/tree/refactor_rigourous_basemodels , in which:
  • [ ] classes will directly sublcass BaseModel
  • [ ] classes will follow schema from openminds
  • [ ] the experiment will start small, with the following classses:
  • [ ] Location
  • [ ] Point
  • [ ] BoundinBox
  • [ ] Space
• Potential issues:
  • [ ] compatibility with openminds (e.g. key such as space_id vs coordinateSpace)
  • [ ] possible to keep the current data structure (e.g. volume.space reference the space instance, useful in python) and openminds compliant (coordinateSpace complies to openminds schema)

[xgui3783]

according to https://github.com/samuelcolvin/pydantic/issues/643 , a 3rd party library https://github.com/koxudaxi/datamodel-code-generator exists to generate pydantic models directly from json schema

[xgui3783]

fixed by #154