[csharp][generichost] Form models

[devhl-labs]

Adds a new PetStore sample with the following appended to the yaml

  skipFormModel: false
inlineSchemaOptions:
  RESOLVE_INLINE_ENUMS: true

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[wing328]

https://github.com/OpenAPITools/openapi-generator/actions/runs/8500781772/job/23288598357?pr=18264 failed.

can you please take a look?

[devhl-labs]

This has to merged first
#18265

[wing328]

just merged that pr