Add Codeowners

[chaospuppy]

@mjnagel:

Might be worth setting up codeowners here for some of the subdirectories. In particular might be something like:

packer/vsphere: owned by @chaospuppy n company (@defenseunicorns/mission-ops-team ?)
packer/nutanix: owned by @jacobbmay n company (@defenseunicorns/digital-salmon ?)
all other files: owned by @defenseunicorns/uds-core
Given the current limited ability to CI test vsphere/nutanix it's probably good to have those owned by teams that have access to > test environments. Also could adjust CI accordingly so that the AWS CI isn't required when only vsphere/nutanix changes are present.

[mjnagel]

I believe the settings are in place for branch protection to ensure codeowner review is required but would be good to validate that once codeowners are in place as well!