Add support for HTTPS remote mounts

[ruimarinho]

Based on cirruslabs/tart#620, it would be great to relax orchard's host dir validation as right now it fails for remote HTTPS mounts:

❯ orchard --version
orchard version 0.14.0-13b4e19

Launching a VM with the remote HTTPS mount:

❯ orchard create vm --image ghcr.io/cirruslabs/macos-ventura-xcode:14.3.1 ventura-xcode --memory 4295 --cpu 2 --headless=false --host-dirs=ghar:https://github.com/actions/runner/releases/download/v2.309.0/actions-runner-osx-arm64-2.309.0.tar.gz
2023/10/11 14:34:11 invalid hostDir specification: hostDir's third part can only be "ro", got "//github.com/actions/runner/releases/download/v2.309.0/actions-runner-osx-arm64-2.309.0.tar.gz"

With :ro:

❯ orchard create vm --image ghcr.io/cirruslabs/macos-ventura-xcode:14.3.1 ventura-xcode --memory 4295 --cpu 2 --headless=false --host-dirs="ghar:https://github.com/actions/runner/releases/download/v2.309.0/actions-runner-osx-arm64-2.309.0.tar.gz:ro"
2023/10/11 14:35:49 invalid hostDir specification: hostDir specification can only contain 3 parts at max