To build the Go client files you have to generate it with OpenAPI generator. This client can be used to access the API within Go projects.
The easiest way to generate the client files is to use one of the predefined generation script which use the OpenAPI Generator Docker image.
.\generate.cmd # Windows
./generate.sh # Linux
If you want to use other generators take the necessary generator options from one of the scripts. See OpenAPI Generator documentation for further details.