Allows `protonvpn-app` to start minimized

[hsiurebgjk]

Addresses: https://protonmail.uservoice.com/forums/932836-proton-vpn/suggestions/45290605-start-protonvpn-minimized-in-tray-linux

Adds two command line options to protonvpn-app:

• --start-minimized
• --version

protonvpn-app --help
Usage:
  protonvpn-app [OPTION…]

Help Options:
  -h, --help                 Show help options
  --help-all                 Show all help options
  --help-gapplication        Show GApplication options
  --help-gtk                 Show GTK+ Options

Application Options:
  --start-minimized          Start minimized in the system tray
  -v, --version              Display the application's version
  --display=DISPLAY          X display to use

Example output with --version

protonvpn-app --version
4.3.2

echo "Exit status: $?"
Exit status: 0

protonvpn-app -v
4.3.2

To start Proton VPN minimized:

protonvpn-app --start-minimized