K8SPG-374 Documented WAL lag detection

[nastena1606]

modified: docs/operator.md
modified: docs/standby-backup.md
modified: docs/standby-streaming.md
modified: docs/standby.md

[Copilot]

Pull request overview

This PR adds comprehensive documentation for WAL lag detection functionality in standby clusters. The feature allows operators to configure a maximum acceptable WAL lag threshold (standby.maxAcceptableLag) and receive clear signals when replication falls behind, helping prevent application downtime during disaster recovery scenarios.

Changes:

• Added new section documenting WAL lag detection feature and its behavior across all standby types
• Updated streaming standby tutorial to include the new optional configuration parameter
• Updated repo-based standby tutorial to include the new optional configuration parameter with known limitations
• Added parameter reference documentation for standby.maxAcceptableLag in the operator configuration guide

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
docs/standby.md	Added comprehensive section explaining WAL lag detection, its effects (pod marked unready, cluster state changes, condition set), and known limitations for repo-based standby
docs/standby-streaming.md	Added maxAcceptableLag parameter to YAML example and bullet-point explanation of its behavior
docs/standby-backup.md	Added reference to lag detection feature with cross-links and commented YAML example showing optional parameter usage
docs/operator.md	Added complete parameter reference for standby.maxAcceptableLag including description, data type, format, and behavior

Comments suppressed due to low confidence (3)

docs/standby.md:21

• There are two consecutive spaces between "The" and "StandbyLagging". This should be a single space for consistency.

* The  `StandbyLagging` condition is set in the cluster status. You can check the conditions with the `kubectl describe pg <cluster-name> -n <namespace>` command.

docs/standby-backup.md:62

• There are two consecutive spaces between "the" and "difference". This should be a single space for consistency.

The configuration of the disaster recovery site is similar [to that of the Main site](#configure-main-site), with the  difference in standby settings.

docs/standby-streaming.md:88

• For consistency with operator.md line 107, consider adding the article "the" before initializing state to read: "the cluster goes into the initializing state". This matches the phrasing used in the operator.md parameter documentation.

* `standby.maxAcceptableLag` (optional) enables replication lag detection. When the WAL lag exceeds this value, the standby primary pod is marked as unready, the cluster goes into `initializing` state, and a `StandbyLagging` condition is set in the status.

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