Add markers for cluster APIs.

[Naarcha-AWS]

Part of issue #9050

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[Naarcha-AWS]

Sent two fixes for cluster parameter descriptions:

• Add description for level parameter in cluster health. opensearch-api-specification#815
• Fix typo in cluster level description opensearch-api-specification#816

These must be merged before this PR can move forward.

[kolchfa-aws]

Some changes to be made in the documentation and in the spec. Thank you.

[kolchfa-aws]

Add an endpoint

[kolchfa-aws]

Add a copy button

[kkhatua]

@Naarcha-AWS would it be possible to have the validation capture this? This almost feels like a checklist is needed... the diffs show the "the default value is ..." translated to "N/A" .
I'm guessing the APISpec should have had this, right? If not, following the process, we'll need to add it as discussed. And for later-planned namespaces, push the onus of this on the Dev teams/