feat(fleet): extract dependencies from helm blocks with OCI-based helm charts

[webD97]

Changes

This PR updates the fleet manager to handle helm charts with OCI-based registries.

Context

Previously, the fleet manager ignored OCI-based helm blocks because they do not set a .repo field. Instead, the .chart field is set to an oci:// URL (see (https://fleet.rancher.io/ref-fleet-yaml)[fleet.yaml docs]. Valid example:

helm:
  chart: oci://registry-1.docker.io/bitnamicharts/external-dns
  version: 7.0.2
  releaseName: external-dns

targetCustomizations:
  - name: target-1
    helm:
      chart: oci://registry-1.docker.io/bitnamicharts/external-dns
      version: 7.0.2

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository: https://github.com/webD97/renovate-testrepo

[renovate-release]

🎉 This PR is included in version 37.292.0 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)
• 37.292.0

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