fix: Fix api_url param to partition_via_api (#2342)
Closes #2340
We need to make sure the custom url is passed to our client. The client
constructor takes the base url, so for compatibility we can continue to
take the full url and strip off the path.
To verify, run the api locally and confirm you can make calls to it.
```
# In unstructured-api
make run-web-app
# In ipython in this repo
from unstructured.partition.api import partition_via_api
filename = "example-docs/layout-parser-paper.pdf"
partition_via_api(filename=filename, api_url="http://localhost:8000")
```
