breaking: Make StepDownOnRemoval the default behavior

[soma00333]

Summary:

This PR addresses issue #83 and is part of the v4.0.0 milestone.

The StepDownOnRemoval feature, introduced in PR #79, ensures that a leader steps down to a follower role after it removes itself from the group or is demoted to a learner. Without this feature, the former leader may continue sending heartbeats despite no longer being part of the group, which could cause inconsistencies.

For backward compatibility, this behavior was initially disabled by default. In version 4.0.0, we aim to make this behavior the default and remove the associated configuration setting to simplify the leadership transition logic.

Key Changes:

• Removed the configurability of StepDownOnRemoval; the behavior is now always enabled.
• Updated the relevant tests to reflect the mandatory StepDownOnRemoval behavior.

Breaking Changes:

This is a breaking change for projects relying on the false configuration of StepDownOnRemoval. The leadership transition behavior will now enforce stepping down when a leader removes itself or is demoted, which may require updates to dependent systems or configurations to align with the new behavior.

Related References:

• related issue: #83
• related pr: #79
• related commit: 72d62a1

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[k8s-ci-robot]

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[soma00333]

@ahrtr
Hello again,
I handled a ticket in the v4.0.0 milestone.
Once the branch is ready, please review this too.
Thank you.