Change `proto1` to operate over stdin

### Context

It's possible with the CLI-only interface for `proto1` that a settings extension command with large JSON values would exceed the max command buffer size on bottlerocket, 128KB.

In order to avoid this issue, we should change `proto1` to accept input from stdin.

### Definition of done

Settings extensions accept the following input mode:

```bash
echo '{"some": "json"}' | extension proto1 set
```