bug(atac): The size of the fragment file is not returned

[Bento007]

Describe the bug

When retrieve a dataset version from the curation API, the filesize of ATAC_FRAGMENT and ATAC_INDEX are wrong.

{'assay': [{'label': '10x multiome', 'ontology_term_id': 'EFO:0030059'}],
 'assets': [{'filesize': -1,
             'filetype': 'ATAC_FRAGMENT',
             'url': 'https://datasets.cellxgene.dev.single-cell.czi.technology/704fa3c5-22dd-4f7b-862a-7a921517d15b-fragment.tsv.bgz'},
            {'filesize': -1,
             'filetype': 'ATAC_INDEX',
             'url': 'https://datasets.cellxgene.dev.single-cell.czi.technology/704fa3c5-22dd-4f7b-862a-7a921517d15b-fragment.tsv.bgz.tbi'},

To Reproduce

Steps to reproduce the behavior:

1. submit an ATAC dataset to a private collection
2. after processing, use the curation API to get the collection version. The filesize will be -1 for ATAC assets.

Expected behavior

the correct size of the fragment files should be returned

[Bento007]

We also need update the portal API here so the frontend can get the asset url. Until this is fix, we can return -1 if the size is not availible