Add support for upx

[dmikusa]

upx is a tool for compressing binary executables. It has some excellent compression ratios and very low runtime overhead. It would be helpful with Rust binaries. We should add support.

The cargo buildpack should follow the pattern established here and optionally run upx to compress output binaries.

The upx buildpack also needs to be added into the Rust composite buildpack/builder. paketo-community/rust#293