REST endpoints do not allow for optional parameters

### Version Information

Server Version: v2.0.10

### Environment

OSS

### What is the expected behaviour?

When creating a rest api endpoint like:

```
query MyQuery($id: uuid) {
companies(where: {id: {_eq: $id}}) {
id
}
}
```

I would like ?id=xxxx to be an optional search parameter (a fairly typical REST pattern). Not specifying an ID simply returns all companies, as I would expect. This worked correctly in Hasura v1 (or with `HASURA_GRAPHQL_V1_BOOLEAN_NULL_COLLAPSE=false`).

### Keywords

REST, optional parameters

### What is the current behaviour?

API endpoint returns `{"path":"$.selectionSet.companies.args.where.id._eq","error":"unexpected null value for type \"uuid\"","code":"validation-failed"}`

This is a problem for any REST API endpoint where you want a parameter to be optional or nullable.

### How to reproduce the issue?

Create above query (or something similar) as a REST API endpoint.
Go to the endpoint without specifying an id parameter
error returns

### Screenshots or Screencast


### Any possible solutions?

Either the Hasura REST API implementation needs work to be able to automatically exclude parameters that are null from the query, or make the default for *queries only* to ignore null parameters. I understand why the change was made to prevent mutations from doing dangerous `delete_users(where: {id: {_eq: null}})` type behaviour, but enforcing that restriction in a place more safe like queries breaks features like REST.