[Feature] Investigate Managed DALEC for fleet-networking image builds

[ytimocin]

Investigate adopting Managed DALEC for fleet-networking image builds. Sync with the team already working on this, file onboard.yml PR if applicable, switch build-publish-mcr.yml over once onboarded.

Mirror of Azure/fleet#1306.

[britaniar]

Onboarding yaml: https://github.com/azure-management-and-platforms/aks-dalec-build-defs/pull/201/changes/f25039d0ca3c7be9b7abf6bdba73c1f9e027f412