[BUG][csharp-netcore] Seems like optionalProjectFile=false isn't used with csharp-netcore

Description

• Executing the following:
  openapi-generator-cli generate -i https://petstore3.swagger.io/api/v3/openapi.json -g csharp-netcore -o api --additional-properties=optionalProjectFile=false,sourceFolder=test
• Same Problem with master: tested with latest master (amd64 - digest on dockerhub: 267dafcbfb97):
  docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:latest generate \ -i https://petstore3.swagger.io/api/v3/openapi.json -g csharp-netcore -o api \ --additional-properties=optionalProjectFile=false,sourceFolder=test \ -o /local/out/csharp
• I found optionalProjectFile only in readmes like this, but not in code: https://github.com/OpenAPITools/openapi-generator/blob/master/docs/generators/csharp-netcore.md
• expected behaviour: at the end of generating der is no Org.OpenAPITools.csproj
• actual behaviour: this flag doesn't change anything, as far as I can see

openapi-generator version

• 6.2.1 (but even master)

Related issues/PRs

• No related found so far

Suggest a fix

• did search through the organisation here with https://github.com/search?p=4&q=org%3AOpenAPITools+optionalProjectFile&type=Code
  • found ~ 30 Code-sources, looked through it which of them belong to csharp-netcore and only found Readme-Files and similar. Code usages only in java-generators.
• No fix so far, but if someone can point me to the right file I may help here

Additional question

• should a solution file get created if I don't want to create a projectFile? I would not expect

Reproduce the command shown in the issue with the csharp-netcore generator, then compare its behavior with docs/generators/csharp-netcore.md, where optionalProjectFile is documented. Locate the csharp-netcore generator entry point and project templates, and verify that optionalProjectFile=false prevents Org.OpenAPITools.csproj generation while checking the expected solution-file behavior.