Compress release binaries

[alexellis]

Compress release binaries using the same approach that inletsctl uses, due to the larger size of binaries including the client-go from Kubernetes.

A quick test showed the 32.9MB binary for Linux was compressed to a 9.5MB tgz file.

https://github.com/inlets/inletsctl/blob/master/Makefile

After updating the Makefile for kubetrim, the tool definition in arkade wll also need to be updated to uncompress the tar/zip depending on the architecture. Again, copy the example of inletsctl in arkade.