B #242: fixes netplan conflict with networkmanager (#244)

- Removes NETCFG_TYPE override on the Ray and Dynamo appliances gen_context scripts for avoiding conflicts between netplan and network manager.

- This caused troubles in ubuntu2404 due to the following network manager changes, creating a network configuration file for eth0 that overrides the one created in the base image for one-context:

  * NetworkManager now uses Netplan as its default settings-storage backend. On upgrade, all connection profiles from /etc/NetworkManager/system-connections/ are transparently migrated to /etc/netplan/90-NM-*.yaml and become ephemeral, Netplan-rendered connection profiles in /run/NetworkManager/system-connections/. Backups of the original profiles are automatically created in /var/lib/NetworkManager/backups/ (read more at NetworkManager YAML settings backend 109 [1] and LP: #1985994 21 [2]).

- We also removed the NETCFG_TYPE override from the example appliance gen_context script.


[1] https://netplan.readthedocs.io/en/stable/netplan-everywhere
[2] https://bugs.launchpad.net/netplan/+bug/1985994



Signed-off-by: Aleix Ramírez <aramirez@opennebula.io>