Parameterize import artifacts dirs

Currently, in the post_init for anything inheriting from AbstractFileArtifact and ContainerArtifact, we're forcing static destination paths as such.

Dest path is set here initially, where it can be set either as a parameter passed to the class, or as an environment variable. I think this is fine since we can still update the path dynamically.

@dataclass
class AbstractArtifact(ABC):
    def __post_init__(self):
        self.dest_path = self.dest_path or pathlib.Path(
            f"{os.environ.get('ARTIFACT_DIR')}"
        )

---

In the following two classes, the final destination dir is set statically to either <base_dest_dir>/external-resources or <base_dest_dir>/images

class AbstractFileArtifact(AbstractArtifact):
    def __post_init__(self):
        super().__post_init__()
        # self.dest_path passed to pathlib is set in AbstractArtifact
        self.dest_path = pathlib.Path(self.dest_path, "external-resources")

and

class ContainerArtifact(AbstractArtifact):
    def __post_init__(self):
        super().__post_init__()
        # self.dest_path passed to pathlib is set in AbstractArtifact
        self.dest_path = pathlib.Path(self.dest_path, "images")

We should allow these fields to be set when initializing the class, rather than enforcing all artifacts need to go into either external-resources and images. We might also want to consider updating this code to make it less confusing how the destination directory is set through inheritance.