api request: asset blob id to asset/dandiset/version

I need to build a map from asset blob id to dandiset(s). Currently, I am doing this by:

```python
client = DandiAPIClient()

with shelve.open("asset_blob_to_dandiset") as db:
for dandiset in tqdm(list(client.get_dandisets()), position=1):
for version in tqdm(list(dandiset.get_versions()), position=2, leave=False):
dandiset = client.get_dandiset(dandiset_id=dandiset.identifier, version_id=version.identifier)
for asset in tqdm(list(dandiset.get_assets()), position=3, leave=False):
blob_id = asset.zarr if ".zarr" in pathlib.Path(asset.path).suffixes else asset.blob
db[blob_id] = dandiset.identifier
```

This works, but feels terrible inefficient because I really only need the map for a subset of assets, but since I don't know which dandisets they belong to I am forced to iterate over all of them in order to create a reverse map. It would be great if I could have an endpoint like `assets/blob/{blob_id}/` which would return asset metadata. Ideally, this would include the ids of each dandiset that contains this asset and versions within each of those dandisets that contain this asset.