Mutli Platform Images: build arm64 images

[a-mnich]

Name: Multi Platform Images
About: switched build workflow to multi platform images

Intention:

I'm running a k8s cluster with arm64 only nodes. As the containerSSH images previously were amd64 only I wasn't able to run it on those nodes. As there are already arm64 binaries building arm64 images is also possible.

Changes

Improvements to Docker and Docker Compose:

• .github/workflows/push.yml and .github/workflows/tag.yml: Updated the Docker Buildx setup to include multi-platform support for linux/amd64 and linux/arm64. "docker-compose" install isn't needed anymore as buildx contains "docker compose" [1] [2]
• docker-compose.yaml: Added platform specifications for linux/amd64 and linux/arm64 to the build contexts for containerssh and containerssh-test-authconfig services. [1] [2]

Updates to build.go script:

• Replaced docker-compose commands with docker compose as docker-compose is legacy and not included in standard buildx installations anymore. [1] [2] [3] [4] [5] [6]
• Introduced a new optional OrganisationVariable field in the registry struct to support organization-specific image naming. This is especially usefull when testing the build with a private registry where the organizational name isn't equal to the username username.

Documentation updates:

• README.md: Updated references from docker-compose to docker compose and revised example environment variable values. [1] [2] [3]

Other changes:

• build.yaml: Dropped build of versions which don't have arm64 binaries
• containerssh-test-authconfig/Dockerfile and containerssh/Dockerfile: Added TARGETOS and TARGETARCH arguments to support multi-platform builds. [1] [2] [3] [4]

Organisational

Are you the owner of the code or do you have permission of the owner?
Yes

The code will be published under the MIT-0 license. Have you read and understood this license?
Yes