feat: add a ghcr.io container artifact for metal-cli releases

[displague]

fixes #122

[displague]

Build failed when I tried this in my fork:

Downloading https://github.com/goreleaser/goreleaser/releases/download/v1.16.1
/goreleaser_Linux_x86_64.tar.gz
Extracting GoReleaser
/usr/bin/tar xz --warning=no-unknown-keyword --overwrite -C /home/runner/work/_temp/203907ad-7430-4da4-b891-e0af8a7f4e18 -f /home/runner/work/_temp/d7ee0456-6a5e-42ef-aee9-254637a19c44
GoReleaser latest installed successfully
/opt/hostedtoolcache/goreleaser-action/1.16.1/x64/goreleaser release --clean
  • starting release...
  • loading config file                              file=.goreleaser.yml
  • loading environment variables
    • using token from "$GITHUB_TOKEN"
  • getting and validating git state
    • building...                                    commit=0e[14](https://github.com/displague/metal-cli/actions/runs/4432294054/jobs/7776174127#step:4:15)9420170219adabaec082ff82de9520f17a43 latest tag=v0.0.9
  • parsing tag
  • setting defaults
  • running before hooks
    • running                                        hook=go mod download
    • running                                        hook=go generate ./...
    • took: 10s
  • checking distribution directory
  • loading go mod information
  • build prerequisites
  • writing effective config file
    • writing                                        config=dist/config.yaml
  • building binaries
    • building                                       binary=dist/metal-cli_freebsd_arm_6/metal
    • building                                       binary=dist/metal-cli_freebsd_amd64_v1/metal
    • building                                       binary=dist/metal-cli_freebsd_arm_7/metal
    • building                                       binary=dist/metal-cli_freebsd_arm64/metal
    • building                                       binary=dist/metal-cli_linux_amd64_v1/metal
    • building                                       binary=dist/metal-cli_linux_arm_6/metal
    • building                                       binary=dist/metal-cli_linux_arm_7/metal
    • building                                       binary=dist/metal-cli_linux_arm64/metal
    • building                                       binary=dist/metal-cli_windows_amd64_v1/metal.exe
    • building                                       binary=dist/metal-cli_windows_arm_6/metal.exe
    • building                                       binary=dist/metal-cli_windows_arm_7/metal.exe
    • building                                       binary=dist/metal-cli_windows_arm64/metal.exe
    • building                                       binary=dist/metal-cli_darwin_amd64_v1/metal
    • building                                       binary=dist/metal-cli_darwin_arm64/metal
    • took: 4m33s
  • generating changelog
    • writing                                        changelog=dist/CHANGELOG.md
  • archives
    • skip archiving                                 binary=metal.exe name=metal-windows-armv6.exe
    • skip archiving                                 binary=metal name=metal-linux-armv6
    • skip archiving                                 binary=metal name=metal-freebsd-armv7
    • skip archiving                                 binary=metal name=metal-freebsd-arm64
    • skip archiving                                 binary=metal.exe name=metal-windows-amd64.exe
    • skip archiving                                 binary=metal name=metal-linux-arm64
    • skip archiving                                 binary=metal.exe name=metal-windows-arm64.exe
    • skip archiving                                 binary=metal name=metal-linux-amd64
    • skip archiving                                 binary=metal name=metal-linux-armv7
    • skip archiving                                 binary=metal.exe name=metal-windows-armv7.exe
    • skip archiving                                 binary=metal name=metal-darwin-amd64
    • skip archiving                                 binary=metal name=metal-darwin-arm64
    • skip archiving                                 binary=metal name=metal-freebsd-armv6
    • skip archiving                                 binary=metal name=metal-freebsd-amd64
  • calculating checksums
  • docker images
  ⨯ release failed after 4m[43](https://github.com/displague/metal-cli/actions/runs/4432294054/jobs/7776174127#step:4:44)s               error=docker build failed: failed to execute image template 'ghcr.io/{{ .Env.GITHUB_REPOSITORY }}:{{ .Tag }}-{{ .Arch }}{{ if .Arm }}v{{ .Arm }}{{ end }}': template: tmpl:1:[51](https://github.com/displague/metal-cli/actions/runs/4432294054/jobs/7776174127#step:4:52): executing "tmpl" at <.Arch>: map has no entry for key "Arch"
Learn more at https://goreleaser.com/errors/docker-build

[cprivitere]

Needs fix for whatever build failure Marques hit. Needs title in line with new standards.