Cannot generate resources if provider is not defined

### tfplugingen-openapi CLI version

```
$ tfplugingen-openapi --version
tfplugingen-openapi module: v0.3.0
```

### OpenAPI Spec File

```YAML
Not useful
```

### Generator Config

```YAML
resources:
container:
create:
path: /containers/v1beta1/regions/{region}/containers
method: post
read:
path: /containers/v1beta1/regions/{region}/containers/{container_id}
method: get
```

### Expected Behavior

I would expect only the resource files to be created

### Actual Behavior

```
tfplugingen-openapi generate --config terraform_generator_config.yml --output ./generated/terraform/scaleway.containers.v1beta1.Api.json ./generated/scaleway-openapi/openapi/scaleway.containers.v1beta1.Api.yml
time=2024-03-28T16:42:15.314+01:00 level=ERROR msg="error executing command" err="error parsing generator config file: config validation error(s):\n\tprovider must have a 'name' property"
make: *** [tf-schemas] Error 1
```

### Additional Information

I would like to have different files, that are targeting different part of the generation. We have many APIs and having everything bundled in a single file is not very interesting.
Also if we are forced to declare provider definition while not being interested in the output it seems to be inefficient

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct