Remote schema, forward headers issue

Hasura 2.0.0-alpha.9

If I select `Forward all headers from client` when setting up remote schema

then if I try to run any query in the console the end result is

```
{
"errors": [
{
"extensions": {
"path": "$",
"code": "remote-schema-error"
},
"message": "Failed reading: not a valid json value"
}
]
}
```
and no requests goes through to the remote.

Reproduce the issue in the Hasura console by configuring a remote schema with “Forward all headers from client” enabled, then running any query. Trace the remote-schema request path and verify that the forwarded headers are handled as valid data; done means the query succeeds and a request reaches the remote schema.

Written by the indexing model from the issue text.