[EPIC] Geo-distributed architecture support for Graviton

### Describe the proposal

> This issue tracks the works of design and implements a geo-distributed HA architecture for Graviton. The owner of this epic should have a design in detail and break down into subtasks.

### Task list

_No response_

Begin by treating this as an architecture-design epic rather than a single code change. Define the geo-distributed high-availability design for Graviton and break the work into concrete subtasks. Done means the design is detailed enough to guide implementation and the subtasks are clearly recorded.

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