Consider mapping JSON schema `date-time` format to `timetypes.RFC3339` custom type

### Use Cases or Problem Statement

JSON schema (the backbone of all the request/response body schemas in OpenAPI 3.0/3.1) supports designating a `type: string` as an RFC3339 string via `format: date-time`: https://json-schema.org/understanding-json-schema/reference/string#dates-and-times.

Recently, HashiCorp has published [terraform-plugin-framework-timetypes](https://pkg.go.dev/github.com/hashicorp/terraform-plugin-framework-timetypes@v0.3.0/timetypes#RFC3339), which contains an `RFC3339` [custom string type](https://developer.hashicorp.com/terraform/plugin/framework/handling-data/types/custom), which provides validation and semantic equality handling that is often required for RFC3339 strings. The Provider code specification already supports [custom types](https://developer.hashicorp.com/terraform/plugin/code-generation/specification#custom_type).

### Proposal

For any string types that define a `format` of `date-time`, add the `timetypes.RFC3339Type` type and `timetypes.RFC3339` value to the custom type in the outputted provider code spec.

#### Schema
```yaml
rfc3339_prop:
description: RFC3339 date-time string!
type: string
format: date-time
```

#### IR Attribute
```json
{
"name": "rfc3339_prop",
"string": {
"computed_optional_required": "computed",
"description": "RFC3339 date-time string!",
"custom_type": {
"import": {
"path": "github.com/hashicorp/terraform-plugin-framework-timetypes/timetypes"
},
"type": "timetypes.RFC3339Type",
"value_type": "timetypes.RFC3339"
}
}
}
```

### Additional Information

_No response_

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