Add support tunnel functionality

[rtertiaer]

Users of AmpliPis ought to have the ability to instantiate a support tunnel connection from their appliances in the field to a Micro-Nova shell server. This will allow us to easily see bugs in the field and shorten the feedback loop between a support request and fix.

This implementation will need to be extremely transparent, privacy preserving and rigorously secure. Any proposed implementation should check these boxes:

• e2e encrypted
• all access to customer appliances requires two factors and explicit customer action to provide access
• the design should not permit customer boxes to access internal micronova resources
• logs of all access & interactions with the appliance should be available for the end user to peruse

more?

[rtertiaer]

A quick sketch of a proposed implementation might look something like this:

• on the amplipi, a form with some details is filled out and a button labelled "start a support tunnel" button is clicked
• amplipi generates a public/private key and passphrase for a wireguard tunnel
• an API server at micronova listens for requests for support. an amplipi POSTs the public key to this service
• the service creates a queue of "support requests" with the details of the support tunnel request
• when a particular item in the queue is approved by a micronova engineer, the service launches a throwaway VM; this then instantiates its own wireguard material and through the API provides that public key back to the amplipi (cons: we may need to spend money. the amplipi probably needs to poll until this key material is available.)
• the passphrase the amplipi generates is provided out of band by the customer in a support request and is used as both the wireguard tunnel PSK and ssh password.
• after a session, .bash_history is uploaded someplace and provided to the end user (this is not a great implementation of the transparency here - would love ideas.)
• the web service (and possibly the appliance itself) reaps all VMs/connections that have been idle for X hrs, or when explicitly closed.