Design and implement packaging process to bundle Rust in signed tar

[alamb]

Note: migrated from original JIRA: https://issues.apache.org/jira/browse/ARROW-12445

The goal of this task is to agree on the strategy and process, and implement it in dev/release , to bundle Rust's source code on the signed tar as part of the arrow release.

Ideas:

1. use the latest published source code in crates.io
2. use a git ref from arrow-rs pointing to the latest release
3. use the source in arrow-rs@master

Some pros and cons:

• [pro] is is downloaded from within ASF
• [pro] it has been released (as it was voted on)
• [con] it is not integration-tested against latest arrow@master, only master at the time of the release

• [pro] it has been officially released (as it was voted on)
• [con] is is downloaded from outside ASF
• [con] it is not integration-tested against latest arrow@master, only master at the time of the release

• [pro] It is the latest
• [pro] it is integration-tested against latest master
• [con] it has not been released in crates.io

[alamb]

This is basically completed here: https://github.com/apache/arrow-rs/blob/master/dev/release/README.md