Change javy-cli to download a specific version of Javy instead of the latest version

[jeffcharles]

Description of the change

Changes javy-cli to download a specific version instead of the current latest released version.

Why am I making this change?

The current behaviour of downloading the latest version of Javy makes it impossible for us to introduce breaking changes to the command line interface in Javy.

Checklist

• [x] I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli and javy-core do not require updating CHANGELOG files.
• [x] I've updated the relevant crate versions if necessary. Versioning policy for library crates
• [x] I've updated documentation including crate documentation if necessary.