cloud-init: T5190: Added Cloud-init pre-configurator

Added a new service that starts before Cloud-init, waits for all network
interfaces initialization, and if requested by config, checks which interfaces
can get configuration via DHCP server and creates a corresponding Cloud-init
network configuration.

This protects from two situations:

• when Cloud-init tries to get meta-data via eth0 (default and fallback variant

for any data source which depends on network), but the real network is connected
to another interface

• when Cloud-init starts simultaneously with udev and initializes the first

interface to get meta-data before it is renamed to eth0 by udev