[Metricbeat] Compare previous/current cluster state in the elasticsearch.shard metricset

[consulthys]

This PR adds logic to compare the cluster state UUID between two runs and only send elasticsearch.shard documents if the cluster state has effectively changed. Doing so not only helps save bandwidth as well as ES resources (CPU, thread pools, etc) but also prevents the indexing_failed counter from increasing upon each HTTP 409.

Proposed commit message

Only index elasticsearch.shard documents if there are changes in the cluster state

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

None, as no new shard documents are indexed unless the cluster state changes.

Related issues

Closes #39058

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @consulthys? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

NOTE: backport-v8.x has been added to help with the transition to the new branch 8.x.

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.