Update configure-network-netplan.mdx

[remyleone]

I think this content should be reworked because it contains deprecated features:

root@foobar-v1-v2:/etc/netplan# netplan apply

** (generate:79635): WARNING **: 08:27:12.718: `gateway4` has been deprecated, use default routes instead.
See the 'Default routes' section of the documentation for more details.

** (process:79634): WARNING **: 08:27:13.700: `gateway4` has been deprecated, use default routes instead.
See the 'Default routes' section of the documentation for more details.

** (process:79634): WARNING **: 08:27:14.084: `gateway4` has been deprecated, use default routes instead.
See the 'Default routes' section of the documentation for more details.

[remyleone]

I also think it should be useful to have verification steps (for instance using a ping), to ensure that the failover ip is configured properly.

[bene2k1]

Fixed in #3542