To add failure domain field in Helix instance ZNode

To make instance rack awareness so that we can achieve high availability later, we can add a simple field called "failureDomain" under /CONFIGS/PARTICIPANT/[instance]. This field can be either written manually or by calling cloud provider metadata APIs like [Azure Instance Metadata Service](https://docs.microsoft.com/en-us/azure/virtual-machines/windows/instance-metadata-service?tabs=linux). After this value is set, the next step is to leverage this failure domain metadata together with [pool-based instance assignment strategy](https://docs.pinot.apache.org/operators/operating-pinot/instance-assignment#pool-based-instance-assignment) to achieve high availability. @mcvsubbu @rkanumul @kishoreg @fx19880617 @daniellavoie

Start by tracing the Helix instance ZNode path /CONFIGS/PARTICIPANT/[instance] and the pool-based instance assignment strategy described in the linked Pinot documentation. Determine how the failureDomain field should be stored, whether Azure Instance Metadata Service population is in scope, and how completion will be verified; the issue does not name source files or tests.

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