Entry initialization with an option that not added to a datapack

[hepengfe]

Is your feature request related to a problem? Please describe.
Every time I create a new ontology entry type, when I implement and test the new entry, I have to add code in DataPack and DataStore to test its behavior or pass CI test. I think we should have an option here such that we can "not adding entry to datapack".

Describe the solution you'd like
solution1: make pack: ContainerType optional and when it is None, we don't add entry to datapack.

Describe alternatives you've considered
solution2: add a boolean parameter skip_add, and when it's True we don't add entry to datapack.

Additional context
We might also want to raise warnings in some places when an entry is standalone and users call some datapack-dependent methods.

[hepengfe]

One issue with either make pack optional or add parameter skip_add is that for ontology subclasses, they all need to have such a parameter/optional datapack therefore it involves a lot of changes and adds complexity.