[feat] move provider configuration into a set of constants

cmd/bitmask-connect/main.go

cmd/bitmask-vpn/main.go

pkg/config/config.go

pkg/helper/darwin.go

pkg/helper/linux.go

pkg/helper/windows.go

pkg/standalone/bonafide.go

pkg/standalone/launcher_linux.go

pkg/standalone/main.go

pkg/systray/config.go

pkg/systray/notificator.go

pkg/systray/run.go

pkg/systray/systray.go