[REQ] [go-server] Add option to enable unknown fields

[moritzschmitz-oviva]

Is your feature request related to a problem? Please describe.

I want to be able to allow unknown fields. The configuration is here: https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/go-server/controller-api.mustache#L596. If using any additional properties, it is not possible any more to remove this line.

Describe the solution you'd like

I would like to have an additional property for disabling disallowUnknownFields.

Describe alternatives you've considered

Manually editing the file after every generation.