Always send coordination metadata in remote state diff

[soosinha]

Description

Coordination metadata contains accepted voting configuration and committed voting configuration.
When the voting configuration changes, the changed accepted voting configuration is sent in publish phase. The follower nodes apply this publish phase cluster state on the lastSeen cluster state in PublicationTransportHandler. In the commit phase, each node set the committed voting configuration using the accepted voting configuration by themselves.
When the next cluster state is published, it does not contain any diff in the voting configuration. This next cluster state update uses lastSeen again to apply the diff due to which the committed voting configuration is still set to an older value.
With local cluster state publication, this issue does not occur as the entire coordination metadata is sent in every diff.
With remote cluster state publication, we can mitigate this in the same way by always sending coordination metadata in the diff.

Related Issues

NA

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 3a1e37f: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[Bukhtawar]

The only concern I see is the additional download overhead(remote store calls) on the follower nodes

[soosinha]

The only concern I see is the additional download overhead(remote store calls) on the follower nodes

I think the long term fix should be to update the lastSeen cluster state in commit phase with the committed config.