Improve ES|QL data federation API docs and examples

[leemthompo]

closes https://github.com/elastic/docs-content-internal/issues/1214

Summary

Improves the documentation experience for the ES|QL data federation APIs added in #6366.

• Adds OpenAPI request and response examples for all six data source and dataset endpoints, covering eight request flows and eight corresponding success responses.
• Marks all six endpoints as Technical Preview; Stack documentation identifies them as added in 9.5.0.
• Uses concise, consistent navigation titles for getting, listing, creating, updating, and deleting data sources and datasets.
• Connects every endpoint to the feature by mentioning ES|QL data federation in the opening description and adding an ES|QL Data Federation learn-more link.
• Clarifies important behavior, including concrete-name versus wildcard misses, atomic dataset deletion, dependent-dataset conflicts, credential redaction, naming requirements, and create-or-replace semantics.
• Adds request examples that generate client samples, including authenticated curl commands that use $ELASTICSEARCH_URL instead of the generic api.example.com fallback.

Testing

• All eight Console request examples were tested against a live Elasticsearch deployment and returned the expected successful responses.
• All eight generated curl examples were independently tested against the same live deployment and returned HTTP 200 with the expected response shapes.
• Curl testing used unique temporary resource names and successfully deleted both resources afterward.
• Confirmed returned data-source credentials use the ::es_redacted:: sentinel.
• Generated 761 language examples with zero conversion errors.
• Regenerated the schema successfully with Node.js 24, including TypeScript output validation.
• Generated both Stack and Serverless documentation OpenAPI definitions and verified their explicit authenticated curl samples.
• Verified all six Stack operations render Technical preview; Added in 9.5.0 and all six Serverless operations render Technical preview.
• Rendered and inspected both Stack and Serverless Bump previews.

Screenshot

[github-actions]

Following you can find the validation changes against the target branch for the APIs.

No changes detected.

You can validate these APIs yourself by using the make validate target.

[l-trotta]

Looks good, thank you! just a nit, to avoid the backport CI failing, could you remove the outputs from the PR? CI will regenerate everything anyways