[driver] Request for Virtualbox support in Linux

*Please describe the question or issue you're facing with "How to set up the driver - Multipass documentation".*

It is a pity that you don't support using VirtualBox as the hypervisor for multipass in Linux. It would make my life easier.

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*Reported from: https://documentation.ubuntu.com/multipass/latest/how-to-guides/customise-multipass/set-up-the-driver/*

Start with the Multipass documentation page at https://documentation.ubuntu.com/multipass/latest/how-to-guides/customise-multipass/set-up-the-driver/ and inspect how Linux hypervisors and drivers are currently supported. The issue is done when Multipass can use VirtualBox as a Linux hypervisor and the driver setup documentation reflects that support.

Written by the indexing model from the issue text.