Enable sandbox mode

[posix4e]

The newest

• Version:
  Of course! "electron-builder": "^19.28.4",

There's discussion at https://forum.snapcraft.io/t/snappy-and-users-and-groups-obsolete/331 on how to enable the snaps to access the sandbox which we need at brave
This allows things like browsers to use user namespaces in its sandbox <Snappy:Fix Released by jdstrand> https://launchpad.net/bugs/1586547
see https://github.com/snapcore/snapd/wiki/Interfaces#browser-support or use 'allow-sandbox: true'.

So the TLDR is we want both of them activated, enable-sandbox and browser-support, but not turned on by default
Major browser manufacturers may want to use.... Use of 'allow-sandbox' will require permission for distro in the public Snap Store at this time