Add ECS known issue for ecs@mappings and fieldless searches

[zmoog]

Update the 8.13 release notes to add a known issue.

Due to changes introduced to support the ecs@mappings component template (see https://github.com/elastic/kibana/pull/174855[elastic/kibana/pull/174855), Fleet no longer includes ECS fields to the integrations' index.query.default_field.

This may affect integrations that rely on fieldless queries (when no field is specified for a query).

This PR updates the 8.13 release notes to

• acknowledge the problem
• inform users that 8.14 is not affected
• suggest a workaround to 8.13 users

Relates elastic/integrations#10848

[github-actions]

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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]

run docs-build

[zmoog]

@kilfoyle, do you think it's okay to link to the public URL of a KB article? The article's author thoroughly summarized the issue and described workaround and solutions. I would love to leverage this work and use it as the source of truth if there are updates.

[kilfoyle]

do you think it's okay to link to the public URL of a KB article?

@zmoog If the KB article is truly public then yes, for sure you can just link to it. That would be ideal.

However, if I'm not mistaken, either some or all KB articles require a Cloud account to view. If that's the case, we'd need the information to be available in the known issue to support users who don't have a Cloud account, and then we can still link to the KB article for reference.

[kilfoyle]

LGTM! 🚀
Thanks for adding this @zmoog. It looks perfect. I added just one super small suggestion.

[zmoog]

@zmoog If the KB article is truly public then yes, for sure you can just link to it. That would be ideal.

You don't need to be a paying customer to read the content, but you will need to log in to Elastic Cloud.

If you think this scenario does not qualify for this document, I can summarize it for the release notes and keep it up to date until we're out of the ecs@mappings issues.

[zmoog]

However, if I'm not mistaken, either some or all KB articles require a Cloud account to view. If that's the case, we'd need the information to be available in the known issue to support users who don't have a Cloud account, and then we can still link to the KB article for reference.

Sorry, I read the first sentence and started responding! 🤦 Continuing here.

The KB articles can be internal only or available to customers. When they're available to customers, they still need an EC account.

I'll summarize the KB article for the release notes and link to the original KB article, mentioning that it requires a free EC account.

[kilfoyle]

I'll summarize the KB article for the release notes and link to the original KB article, mentioning that it requires a free EC account.

Sounds perfect! And everything looks good. Thanks for looking after this @zmoog!