Exposed and documented new fields creation_date and tier_preference for Elasticsearch integration

[3kt]

Proposed commit message

This change documents the new tier_preference and creation_date index fields for the Elasticsearch integration.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs. N/A no change was made here
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines. No change made here
• ~I have verified that any added dashboard complies with Kibana's Dashboard good practices ~ N/A no change made here

Author's Checklist

• Requires Additional stats fields for Elasticsearch beats#41652 to be merged first
• Pre-requisite for [elasticsearch] Extension of the Elasticsearch integration with datastream-centric stats #11656

How to test this PR locally

By itself, this change doesn't change anything to the behavior of the integration, it will just modify the documentation.

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 19dce61e4c2a2f5b19195d1692a6adf1d50902b8

History

• 💔 Build #19507 failed 575d4fa09290d7e57771f92dfb7efad16553eb05
• 💔 Build #19506 failed 9f0f7c2b7f1937dcc815c05c30a14b39845db142
• 💔 Build #19505 failed dd3072a413cce440bbee57f434b31ab243e9d069
• 💔 Build #18985 failed 01e2fd9d6eac3be8aec91d933f7307fd4ad99f86
• 💔 Build #18957 failed f8ca911ba55c598947b0e233926b1a49799fe4d4

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[3kt]

Closing in favor of #11656