Fix and improve environment variable resolution in repositories

[rocketraman]

Resolves https://github.com/kscripting/kscript/issues/402.

The manual tests for an authenticated repo were not complete.

Fixed and improved the test artifactory server startup.

Added a manual test for environment variable substitution (test 4).

Added a manual test for environment variable substitution with packaging (test 5).

Fix docs for env var substitution to use $FOO rather than {{FOO}} to be compatible with the Kotlin Script backend.