Add known issues about fieldless searches

docs/en/ingest-management/release-notes/release-notes-8.13.asciidoc

@@ -90,6 +90,23 @@ This issue has been link:https:/elastic/elastic-stack-installers/pul
 
 ====
 
+[[known-issue-242-8.13.0]]
+.ECS fields are not included to the `index.query.default_field` in {agent} integrations
+[%collapsible]
+====
+
+*Details*
+
+Due to changes introduced to support ecs@mappings component template (see link:https:/elastic/kibana/pull/174855[elastic/kibana/pull/174855]), {fleet} no longer include ECS fields to the integrations' `index.query.default_field`. This may affect integrations that rely fieldless queries (when no field is specified for a query).
+
+*Impact* +
+
+In version 8.14.0 and later, the {fleet} sets `index.query.default_field` to `*`, so agentless queries will work as expected. We recommend users of {fleet} to upgrade to 8.14 when that release becomes available.
+
+If you are unable to upgrade to 8.14.0, you can follow the workaround described in the link:https://support.elastic.co/knowledge/bbdbeb57.
+
+====
+
 [discrete]
 [[bug-fixes-8.13.2]]
 === Bug fixes
@@ -127,6 +144,23 @@ This issue has been link:https:/elastic/elastic-stack-installers/pul
 
 ====
 
+[[known-issue-242-8.13.0]]
+.ECS fields are not included to the `index.query.default_field` in {agent} integrations
+[%collapsible]
+====
+
+*Details*
+
+Due to changes introduced to support ecs@mappings component template (see link:https:/elastic/kibana/pull/174855[elastic/kibana/pull/174855]), {fleet} no longer include ECS fields to the integrations' `index.query.default_field`. This may affect integrations that rely fieldless queries (when no field is specified for a query).
+
+*Impact* +
+
+In version 8.14.0 and later, the {fleet} sets `index.query.default_field` to `*`, so agentless queries will work as expected. We recommend users of {fleet} to upgrade to 8.14 when that release becomes available.
+
+If you are unable to upgrade to 8.14.0, you can follow the workaround described in the link:https://support.elastic.co/knowledge/bbdbeb57.
+
+====
+
 [discrete]
 [[enhancements-8.13.1]]
 === Enhancements
@@ -233,6 +267,23 @@ This issue has been link:https:/elastic/elastic-stack-installers/pul
 
 ====
 
+[[known-issue-242-8.13.0]]
+.ECS fields are not included to the `index.query.default_field` in {agent} integrations
+[%collapsible]
+====
+
+*Details*
+
+Due to changes introduced to support ecs@mappings component template (see link:https:/elastic/kibana/pull/174855[elastic/kibana/pull/174855]), {fleet} no longer include ECS fields to the integrations' `index.query.default_field`. This may affect integrations that rely fieldless queries (when no field is specified for a query).
+
+*Impact* +
+
+In version 8.14.0 and later, the {fleet} sets `index.query.default_field` to `*`, so agentless queries will work as expected. We recommend users of {fleet} to upgrade to 8.14 when that release becomes available.
+
+If you are unable to upgrade to 8.14.0, you can follow the workaround described in the link:https://support.elastic.co/knowledge/bbdbeb57.
+
+====
+
 [discrete]
 [[new-features-8.13.0]]
 === New features