Data Streams: Add ecs@mappings disclaimer for index templates cloned on ES < 8.13

[zmoog]

Motivation

Starting from version 8.13, Elasticsearch includes the ecs@mappings component templates in all the index templates used in Elastic Agent integrations.

As integrations adopt the ecs@mappings component template, index templates cloned following the "Tutorial: Customize data retention policies" may start having problems with mappings.

End users must update their cloned index templates by adding the ecs@mappings component template.

Change description

This PR added a note and instructions to the tutorial users about updating the cloned index template they created following this tutorial.

Additional Notes

• relates: Add reference to ecs@mappings for each index template kibana#174855

Reviewer checklist

• PR address a single concern.
• PR title and description are appropriately filled.
• Changes will be merged in main.

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[mergify]

This pull request does not have a backport label. Could you fix it @zmoog? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-/d./d is the label to automatically backport to the /d./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[zmoog]

@lucabelluccini @ishleenk17, I'm updating the original tutorial with instructions to update the cloned index templates.

[kilfoyle]

LGTM! Thanks a lot for adding this @zmoog!

[lucabelluccini]

Thank you @zmoog for the docs update!

BTW, this is somehow a breaking change for such users.
I would really invite integration development team & ingest/fleet on how to tackle this in the future automatically.

This is something Platform Ingest (or even further to Elasticsearch) should help to overcome.

[zmoog]

Only those with write access to this repository can merge pull requests.

Is seems I can't merge the PR 😇

[kilfoyle]

Is seems I can't merge the PR 😇

Oops! I forgot about that. I'll merge and make sure the backports are merged too.