Revise gencerts.sh

[sysnet4admin]

What is missing? gencerts.sh is not in the main of custom-metrics-api anymore.

Why do we need it? prometheus-adapter leverage this script but it looks like out of version.

Environment

• kube-prometheus version: release-0.10 and v1.23 for k8s

Anything else we need to know?: If it could revise, I would like to suggest to check golang installed whether or not in here.

# Detect if we are on mac or should use GNU base64 options
case `uname` in
        Darwin)
            b64_opts='-b=0'
            if ! command -v go &> /dev/null ; then 
              brew install golang    
            fi                                    
            ;; 
        *)
            b64_opts='--wrap=0'
            if ! command -v go &> /dev/null ; then 
              apt-get or yum or others like below
            fi
            ;; 
esac

OS checked script sample in linux distro.

It is just suggestion. so feel free let me know. Thank you for your understanding in advance as well.