Implement Brave VPN on Linux

[bsclifton]

Description

Part of parent issue #15804

The goal here would be to create an implementation in brave-core which handles VPN on Linux. Each OS can provide an OS specific implementation for a "VPN Service".

This would need the ability to:

• Create a VPN connection with the OS.
• Update a connection (if details change)
• Connect to the VPN
• Disconnect from the VPN
• Remove the VPN connection from the OS

Windows and macOS which have an somewhat standard way to add a VPN connection - Linux hasn't been completely solved (yet). It would be great if there is a native way to do this

I was able to get something working using strongSwan which we'd need to be careful when integrating with (to ensure compliance w/ licensing). Using compiled binaries and a test VICI client I was able to establish a VPN connection (and we could potentially package these binaries / make available via component updater)

[iam-cult]

I would assume that whatever implementation this uses, it will be broken in both the snap and flatpak packages. Is that the case? Should the feature be disabled in those package formats, or is there some way to work around the sandbox restrictions? I know that the flatpak is unofficial, but since this has not been implemented yet I won't be opening an issue there until this hits stable.

[bsclifton]

Blocked on #23348

[bsclifton]

I think the SKU SDK issue is solved now - needs retesting. We should be able to solve this as we make progress with #29253

[bsclifton]

Removed blocked tag as SKU SDK works on Linux now