timescale / patroni / 9500713889

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Make member xlog updates frequency configurable in K8s

In the past, Patroni had to update the member key every `loop_wait` interval to prevent its disappearance due to TTL. In Kubernetes, the member key won't disappear, however, Patroni still updates it regularly to propagate current xlog location.

Make those updates configurable. If `kubernetes.xlog_cache_ttl` is set to a positive value and no other member data (i.e. role or timeline) changes, do not update the member pod annotation more frequently than the value of `xlog_cache_ttl` seconds.

This reduces the load on the K8s API, as we don't have to update the pod every loop_wait interval. 

If the member needs to be updated due to other reasons (i.e. role change), the xlog position is set to the up-to-date one received from Postgres.

When DEBUG logging is turned on, Patroni will emit log messages similar to the one below when the xlog-only update is withheld because of this parameter:

```
2024-06-06 11:34:36,308 DEBUG: prevented pod update, keeping cached xlog value for up to 10 seconds
```

This parameter is set to 0 by default, so this feature is disabled unless turned on explicitly by the user. The maximum value is 3600s.

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