[csharp] useDateTimeOffset is ignored and datetimes are always generated as "DateTime?"

Created by: rubms

Description

The useDateTimeOffset configuration property is ignored and datetimes are always generated as DateTime?. The expected behavior is to get DateTimeOffset? when useDateTimeOffset=true and DateTime? when useDateTimeOffset=false.

This happens for both: operation parameters and object properties.

openapi-generator version

Error reproduced with openapi generator v3.3.3. The v3.3.2 version worked fine.

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  description: "Spec for testing the generation of DateTime properties"
  version: 1.0.0
  title: DateTime test case.
paths:
  /pets:
    get:
      operationId: getPets
      summary: Pets.
      description: |
        Get pets.
      parameters:
      - name: registrationDateTime
        in: query
        description: "Test datetime query parameter"
        required: false
        schema:
          type: string
          format: date-time
      tags:
      - Pets
      responses:
        200:
          description: Successful request.

Command line used for generation

java -jar openapi-generator-cli-3.3.3.jar generate -g csharp -i test.yml -o test

Additionally, the configuration property useDateTimeOffset is set to true:

{
	"useDateTimeOffset": "true"
}

Steps to reproduce

Generate a C# client using the csharp generator and specifying useDateTimeOffset to true. Any date-time value will be generated as DateTime?, instead of DateTimeOffset?.