Port VMware OEM setup to systemd-sysext image #1144
Description
As was already done for the Azure OEM setup in #769 we want to port VMware over to benefit from updates.
A benefit of sysext images is that they can have a strict coupling to the Flatcar VERSION_ID which enables to use dynamical linking to save space and make the OEM tool packages simpler.
The base Ignition configuration is not needed anymore because the sysext's OEM files already become part of the /usr hierarchy and systemd services there can get started through an Upholds= drop-in.
The migration action has to be defined in the update_engine flatcar-postinst hook like it was done for Azure.