Add additional Packaging options

[ccremer]

• This configures Goreleaser so that it also builds RPM and DEB packages as additional installation methods.
• Also signs the checksum file so users can verify the downloads. The GPG private key is already configured in the settings and in our password DB

Installation and removal become as easy as
sudo rpm -i https://github.com/appuio/seiso/releases/download/<version>/seiso_linux_amd64.rpm
or apt-get remove seiso
or with Ansible:

- name: Install a .deb package from the internet.
  apt:
    deb: https://github.com/appuio/seiso/releases/download/<version>/seiso_linux_amd64.deb`

Example output:

$ goreleaser release --snapshot --rm-dist                                 
   • releasing using goreleaser 0.131.1...
   • loading config file       file=.goreleaser.yml
   • running before hooks
      • running go vet ./...
      • running go test --cover ./...
   • loading environment variables
      • pipe skipped              error=publishing is disabled
   • getting and validating git state
      • releasing v0.5.0, commit adf1ebf2b80fa0b818aa42521b4eb43c695689d8
      • pipe skipped              error=disabled during snapshot mode
   • parsing tag      
   • setting defaults 
      • snapshoting      
      • github/gitlab/gitea releases
      • project name     
      • building binaries
      • archives         
      • linux packages   
      • snapcraft packages
      • calculating checksums
      • signing artifacts
      • docker images    
      • artifactory      
      • blobs            
      • homebrew tap formula
      • scoop manifests  
   • snapshoting      
   • checking ./dist  
      • --rm-dist is set, cleaning it up
   • writing effective config file
      • writing                   config=dist/config.yaml
   • generating changelog
      • pipe skipped              error=not available for snapshots
   • building binaries
      • building                  binary=dist/seiso_darwin_386/seiso
      • building                  binary=dist/seiso_linux_arm64/seiso
      • building                  binary=dist/seiso_linux_amd64/seiso
      • building                  binary=dist/seiso_linux_386/seiso
      • building                  binary=dist/seiso_darwin_amd64/seiso
      • building                  binary=dist/seiso_linux_arm_7/seiso
   • archives         
      • skip archiving            binary=seiso
      • skip archiving            binary=seiso
      • skip archiving            binary=seiso
      • skip archiving            binary=seiso
      • skip archiving            binary=seiso
      • skip archiving            binary=seiso
   • linux packages   
      • creating                  arch=i386 file=dist/seiso_linux_386.deb package=seiso_linux_386.deb
      • creating                  arch=amd64 file=dist/seiso_linux_amd64.rpm package=seiso_linux_amd64.rpm
      • creating                  arch=armhf file=dist/seiso_linux_arm.rpm package=seiso_linux_arm.rpm
      • creating                  arch=arm64 file=dist/seiso_linux_arm64.rpm package=seiso_linux_arm64.rpm
      • creating                  arch=armhf file=dist/seiso_linux_arm.deb package=seiso_linux_arm.deb
      • creating                  arch=i386 file=dist/seiso_linux_386.rpm package=seiso_linux_386.rpm
      • creating                  arch=amd64 file=dist/seiso_linux_amd64.deb package=seiso_linux_amd64.deb
      • creating                  arch=arm64 file=dist/seiso_linux_arm64.deb package=seiso_linux_arm64.deb
   • snapcraft packages
   • calculating checksums
      • checksumming              file=seiso_linux_arm64.deb
      • checksumming              file=seiso_darwin_amd64
      • checksumming              file=seiso_linux_armv7
      • checksumming              file=seiso_darwin_386
      • checksumming              file=seiso_linux_arm.deb
      • checksumming              file=seiso_linux_386
      • checksumming              file=seiso_linux_386.deb
      • checksumming              file=seiso_linux_arm.rpm
      • checksumming              file=seiso_linux_arm64.rpm
      • checksumming              file=seiso_linux_amd64.deb
      • checksumming              file=seiso_linux_386.rpm
      • checksumming              file=seiso_linux_amd64.rpm
      • checksumming              file=seiso_linux_arm64
      • checksumming              file=seiso_linux_amd64
   • signing artifacts
      • signing                   cmd=[gpg -u 51C334321C8CE7A36688DEB45A2CE60942C3A798 --output dist/checksums.txt.sig --detach-sign dist/checksums.txt]
   • docker images    
      • building docker image     image=docker.io/appuio/seiso:vv0.5.0-snapshot
      • pipe skipped              error=publishing is disabled
   • publishing       
      • pipe skipped              error=publishing is disabled
   • release succeeded after 113.19s

I think this would help us gaining popularity with increased installability.

[bittner]

Looks good to me!

I'd need to understand the role of the --skip-sign during builds, all the rest seems good for merging.