appsync-alpha: Schema.fromAsset drops field defaults

### Describe the bug

Using the Schema.fromAsset on a valid graphql schema file will result in default values for fields being dropped.

### Expected Behavior

Default values are maintained in the deployed schema

### Current Behavior

Default values are lost

### Reproduction Steps

1. Declare input values with valid defaults in a graphql schema file
2. Utilize Schema.fromAsset to deploy the schema
3. Review the deployed schema in the console, defaults are now missing

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### CDK CLI Version

2.36.0

### Framework Version

_No response_

### Node.js Version

18.3.0

### OS

Ubuntu 20.04

### Language

Java

### Language Version

11

### Other information

_No response_