Add the cookie setting for Golang code generator

[LinuxSuRen]

The cookie setting is a new feature, but it is not been implemented in the Golang code generator. See also the following screenshots:

you might need to update the following files:

• https://github.com/LinuxSuRen/api-testing/blob/master/pkg/generator/data/main.go.tpl
• https://github.com/LinuxSuRen/api-testing/blob/master/pkg/generator/golang_generator.go

What you need to know

• Golang basic syntax
• Golang template
• Golang HTTP releated SDK

[LinuxSuRen]

completed at #363