Clarify documentation of return format for /v1/querybatch API

According to the Swagger documentation at https://osv.dev/docs/#operation/OSV_QueryAffectedBatch the endpoint `https://api.osv.dev/v1/querybatch` should return a list of `osvVulnerability`.

Instead it returns a list of vulnerability IDs without any vulnerability details or the actual link to the package the vulnerability belongs to.

This leads to the following issues:
- The batch endpoint does not return the OSV format, leading to clients having a need to query those vulnerability IDs. This completely goes against the idea of having a batch endpoint where you get all info for a set of libraries in a single HTTP request so that you do not overload the service.
- It is unclear and undocumented how the current response from the batch endpoint should be used. How to link these vulnerability IDs to the actual packages that were provided in the request?
- The documentation and implementation are out of sync

Example:
```
cat <