Enable active-standby mode for Thanos ruler

[prasadrajesh]

Is your proposal related to a problem?

Two active pods of thanos-ruler are causing high CPU usage on Thanos-query and Thanos-Receiver. So, I want to keep running one pod of thanos-ruler as active mode and other pod should be keep run in standby mode.

Describe the solution you'd like

Need leader selection feature on Thanos-ruler so, at a time only one pod is in active mode.

Describe alternatives you've considered

Additional context

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