Don't require the cloud-config header for meta-data and network-config

[sil2100]

I got reports that people now have issues building image as we became a bit too strict. Tried finding in cloud-init documentation if the #cloud-config header is needed for other than user-data, but didn't see anything. And truth is that it seems to work as-is when they don't.

I think it makes sense to, for now, be less strict and merge this to at least not break existing users.

[codecov]

Codecov Report

Merging #149 (75bac4a) into main (6193013) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #149   +/-   ##
=======================================
  Coverage   89.17%   89.17%           
=======================================
  Files          11       11           
  Lines        2449     2449           
=======================================
  Hits         2184     2184           
  Misses        244      244           
  Partials       21       21           

Files	Coverage Δ
internal/statemachine/classic_states.go	97.86% <100.00%> (ø)

[upils]

LGTM. I took a look at the cloud-init code and indeed it seems that only the user data requires the #cloud-config header (see https://cloudinit.readthedocs.io/en/latest/explanation/format.html)