build: support for building docker image on multiple platforms

[sfat]

• Add support for building docker image on multiple platforms like linux/arm64, besides default linux/amd64
• make use of docker/login-action@v3 and docker/build-push-action@v5 for docker login/build and push

current latest xk6 docker image:

docker run --rm -e GOOS=darwin -e CGO_ENABLED=1 -u "$(id -u):$(id -g)" -v "$PWD:/xk6" \
            grafana/xk6 build master \
            --with github.com/mostafa/xk6-kafka \
            --with github.com/grafana/xk6-output-influxdb@bump-k6

Time duration:

time    0.05s user 0.04s system 0% cpu 3:36.35 total

custom image created specifically for arm64:

docker run --rm -e GOOS=darwin -e CGO_ENABLED=1 -u "$(id -u):$(id -g)" -v "$PWD:/xk6" \
            xk6-andrei build master \
            --with github.com/mostafa/xk6-kafka \
            --with github.com/grafana/xk6-output-influxdb@bump-k6

Time duration:

time  0.04s user 0.03s system 0% cpu 33.783 total

[CLAassistant]

All committers have signed the CLA.

[sfat]

seems that there's another PR already for this. closing this one