Pass image tag as build argument

[nluaces]

Fixes #2442

[pwright]

@nluaces working from your branch:

$ make build-cli
GOOS=linux GOARCH=amd64 go build -ldflags="-s -w  -X github.com/skupperproject/skupper/internal/version.Version="  -o skupper ./cmd/skupper
$ ./skupper version

ie no version

Is the intention that devs must do something like:

export IMAGE_TAG=fix-big-bug  
export REGISTRY=quay.io/yourname   # if pushing images  
  
make build-cli  
make docker-build  
make podman-push

Maybe this shows we need a CONTRIBUTING.md

[nluaces]

ie no version

@pwright that was wrong, thanks for noticing.
I was checking how the version was set while generating the docker image, but I've missed this.

[fgiorgetti]

LGTM