Add upx tool

[bhuisgen]

Add upx tool to compress binary & docker images.

To enable it, add a post hook to your goreleaser build:

builds:
  - hooks:
      post:
        - upx "{{.Path}}"

[troian]

thanks @bhuisgen, does it compress docker images? I thought it only does binaries

[bhuisgen]

Only the binaries files are compressed with upx. Normally images compression is done by docker push before uploading and it depends of the registry too (the docker DTR did it). If you execute a docker save command on your image, it will be compressed like a tarball. I will probably do this by filtering artifacts.json after goreleaser execution.

[caarlos0]

fwiw, if you compress the binary with upx, and your docker image just copies your binary somewhere, then there won't be much more to compress I think...

[troian]

i think the best would be to just install upx any time it will be used.