Support to configure http setting via server

Add support to configure http-client settings on the server

```graphql
schema @server(http: {
  keepAliveInterval: 1,
  keepAliveTimeout: 1
  keepAliveWhileIdle: true,
  poolIdleTimeout: 1024
  poolMaxIdlePerHost: 100
}) {
  query: Query
  mutation: Mutation
}
```

Use these settings while configuring `http_client.rs`