Implement a Hegel metadata API

[chrisdoherty4]

We've concluded the existing metadata endpoints provided by Hegel align with Equinix and that we should maintain this set of endpoints. We do, however, wish to develop a stand-alone metadata standard that compliments Tinkerbell's goals and addresses some challenges observed in the Tinkerbell provisioning.

This ticket is for tracking. A separate design proposal is being written.

[chrisdoherty4]

https://github.com/tinkerbell/proposals/tree/main/proposals/0027