Output version

Unless this is already possible, I wanted to suggest adding a command to output the ODK Validate version. This would be helpful to use on validate.enketo.org.

The issue does not name a file, test, or command entry point. Start by locating the application's command entry point and how its version is stored or exposed; the work is done when a command reliably prints the ODK Validate version, including when used through validate.enketo.org.

Written by the indexing model from the issue text.