multi-arch support

[ozbillwang]

could we support other platforms?

 > [linux/s390x  6/17] RUN helm plugin install https://github.com/databus23/helm-diff && rm -rf /tmp/helm-*:
#0 2.445 mkdir: can't create directory '': No such file or directory
#0 2.484 No prebuild binary for linux-s390x.
#0 2.485 Failed to install helm-diff
#0 2.486        For support, go to https://github.com/databus23/helm-diff.
#0 2.489 Error: plugin install hook for "diff" exited with error

I am interesting on these platfoms:

linux/amd64,linux/arm/v7,linux/arm64/v8,linux/arm/v6,linux/ppc64le,linux/s390x

only amd64 and arm64 are available now.