Add CLI Tool support for OpenAPI Generator pass through commands

[christianhelle]

The changes here add the openapi-generator command to rapicgen for generating code using any supported generator by OpenAPI Generator behind the scenes (https://openapi-generator.tech/docs/generators)

Usage: rapicgen [command] [options]

Options:
  -v|--verbose       Show verbose output
  -?|-h|--help       Show help information.

Commands:
  csharp             Generate C# API client
  jmeter             Generate Apache JMeter test plans
  openapi-generator  Generate code using OpenAPI Generator.
                     See supported generators at https://openapi-generator.tech/docs/generators/
  typescript         Generate TypeScript API client

Run 'rapicgen [command] -?|-h|--help' for more information about a command.

[sonarcloud]

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