Missing functionalities for artefact store

Currently, `artefacts.py` does not explicitly have methods for creating a new collection and filtering collections with filenames. So this additional method is needed for class ArtefactStore:

def filter_create_new(self, existing_collection: Optional [Union[str, ArtefactSet]], filenames: Optional[Union[Path, str, Iterable[Path], Iterable[str]]], new_collection: str):

This would enable the users to

1. Specify the files they want with filenames, filter an existing collection with the filenames and then return a new collection that is a subset of the existing collection.
2. Create an empty collection if the optional arguments are not set.

User cases of this would be like pass a collection to sourcegetter of a new psyclone step.

Start in artefacts.py at the ArtefactStore class and inspect how collections are created and filtered. Check the sourcegetter use case described for a new psyclone step. Done means filter_create_new can select filenames from an existing collection and create a new subset, or create an empty collection when the optional arguments are omitted.

Written by the indexing model from the issue text.