Missing import of github.com/antihax/optional

Description

Swagger-codegen version

Swagger declaration file content or url

Proprietary

Command line used for generation

wget https://repo1.maven.org/maven2/io/swagger/swagger-codegen-cli/2.4.26/swagger-codegen-cli-2.4.26.jar -O swagger-codegen-cli.jar

java -jar swagger-codegen-cli.jar generate -i ../docs/swagger.json -l go -o tmp/

Steps to reproduce

Running the above commands on your swagger.json specification will produce an api_file which uses the package "github.com/antihax/optional" but does not import it.

Related issues/PRs

Referenced in:
https://github.com/swagger-api/swagger-codegen/issues/10213
https://github.com/fintechstudios/ververica-platform-k8s-operator/blob/master/README.md

the people in both of the above comments treated this as a bug to be fixed manually.

Suggest a fix/enhancement

This seems to be the template used:
https://github.com/swagger-api/swagger-codegen/blob/751e59df060b1c3ecf54921e104f2086dfa9f820/modules/swagger-codegen/src/main/resources/go/api.mustache

Start with modules/swagger-codegen/src/main/resources/go/api.mustache and reproduce the issue using the documented swagger-codegen-cli command with the Go generator. Inspect the generated api_file and verify that generated code using github.com/antihax/optional also includes the required import and remains buildable.