feat(vultr): add override for network interface detection

[andy191x]

Proposed Commit Message

feat(vultr): add override for network interface detection (#5847)

Additional Context

The purpose of this feature is to provide the Vultr team with a way to define custom NIC lists to scan for metadata. This is particularly useful when dealing with niche hardware deployments.

The feature checks for the presence of an /opt/vultr/find_candidate_nics.sh shell script on the running guest image. If detected, DataSourceVultr uses that as an optional source of truth before falling back to net.find_candidate_nics().

Test Steps

This feature was tested manually on Vultr's Ubuntu 22.04 and Ubuntu 24.04 images (as of 10/2024).

The added functionality is low risk, as it is both opt-in and limited to the Vultr cloud.

cp vultr.py /usr/lib/python3/dist-packages/cloudinit/sources/helpers/vultr.py
cloud-init clean -r

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)