lisafs is only supported in VFS2. Added a runsc flag which enables lisafs.
When the flag is enabled, the gofer process and the client communicate using
lisafs protocol instead of 9P.
Added a filesystem option in fsimpl/gofer which indicates if lisafs is being
used. That will be used to gate lisafs on the gofer client.
Note that this change does not make the gofer client use lisafs just yet.
Updates #5465
PiperOrigin-RevId: 397917844