path in assets GET could be a regex or substring filtering

it would be nice to be able to filter quickly on items in a dataset by any substring. technically on the db side this should be a simple query on the path column.

instead of
```
https://api.dandiarchive.org/api/dandisets/000003/versions/draft/assets/?path=sub-YutaMouse20
```
we should also be able to do:
```
https://api.dandiarchive.org/api/dandisets/000003/versions/draft/assets/?path=YutaMouse20
```
and
```
https://api.dandiarchive.org/api/dandisets/000003/versions/draft/assets/?path=behavior
```

one possibility is to change `path` to `path-contains`