[enhancement]: Support V1/V2 network-config via nocloud-net with custom webserver

# Enhancement

When nocloud-net is [reading the seed data](https://github.com/canonical/cloud-init/blob/441d8f818de7e08836f43d1b9a1a4418f341b1a5/cloudinit/util.py#L1015), it doesn't read the `network-config` file as specified at the bottom of [the NoCloud docs](https://cloudinit.readthedocs.io/en/latest/reference/datasources/nocloud.html). Even though supporting this would involve reconfiguring the network after it has already come up, there is no reason why this couldn't be done.

# Original Description
Why can't I specify the network-config using this method?
If a drive is mounted with the network-config file, this works.

Is there any reason why the custom webserver method (nocloud-net) does not support this?

See https://cloudinit.readthedocs.io/en/latest/reference/datasources/nocloud.html