[9.0] [Docs] Reproduce #209403 in new API docs (#216439) (#216692)

# Backport

This will backport the following commits from `main` to `9.0`:
- [[Docs] Reproduce #209403 in new API docs
(#216439)](https://github.com/elastic/kibana/pull/216439)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT
[{"author":{"name":"florent-leborgne","email":"florent.leborgne@elastic.co"},"sourceCommit":{"committedDate":"2025-04-01T16:21:43Z","message":"[Docs]
Reproduce #209403 in new API docs (#216439)\n\nThis change reproduces
the asciidoc change made
in\nhttps://github.com/elastic/kibana/pull/209403 into the new API
docs.\nIt'll be picked up the next time the API docs output is generated
and\nrefreshed.\n\n---------\n\nCo-authored-by: kibanamachine
<42973632+kibanamachine@users.noreply.github.com>","sha":"b7d1141b6b4e565647c30eac79773d5cf973724e","branchLabelMapping":{"^v9.1.0$":"main","^v8.19.0$":"8.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:Docs","release_note:skip","v9.0.0","docs","APIDocs","backport:version","v9.1.0"],"title":"[Docs]
Reproduce #209403 in new API
docs","number":216439,"url":"https://github.com/elastic/kibana/pull/216439","mergeCommit":{"message":"[Docs]
Reproduce #209403 in new API docs (#216439)\n\nThis change reproduces
the asciidoc change made
in\nhttps://github.com/elastic/kibana/pull/209403 into the new API
docs.\nIt'll be picked up the next time the API docs output is generated
and\nrefreshed.\n\n---------\n\nCo-authored-by: kibanamachine
<42973632+kibanamachine@users.noreply.github.com>","sha":"b7d1141b6b4e565647c30eac79773d5cf973724e"}},"sourceBranch":"main","suggestedTargetBranches":["9.0"],"targetPullRequestStates":[{"branch":"9.0","label":"v9.0.0","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/216439","number":216439,"mergeCommit":{"message":"[Docs]
Reproduce #209403 in new API docs (#216439)\n\nThis change reproduces
the asciidoc change made
in\nhttps://github.com/elastic/kibana/pull/209403 into the new API
docs.\nIt'll be picked up the next time the API docs output is generated
and\nrefreshed.\n\n---------\n\nCo-authored-by: kibanamachine
<42973632+kibanamachine@users.noreply.github.com>","sha":"b7d1141b6b4e565647c30eac79773d5cf973724e"}}]}]
BACKPORT-->

Co-authored-by: florent-leborgne <florent.leborgne@elastic.co>
Co-authored-by: Lisa Cawley <lcawley@elastic.co>

oas_docs/output/kibana.yaml

@@ -43226,7 +43226,8 @@ paths:
   /api/upgrade_assistant/reindex/batch:
     post:
       description: |
-        Start or resume multiple reindexing tasks in one request. Additionally, reindexing tasks started or resumed via the batch endpoint will be placed on a queue and run one-by-one, which ensures that minimal cluster resources are consumed over time.
+        Start or resume multiple reindexing tasks in one request. Additionally, [reindexing](https://www.elastic.co/docs/api/doc/kibana/operation/operation-start-upgrade-reindex) tasks for upgrading indices that are started or resumed via the batch endpoint will be placed on a queue and executed one-by-one. This ensures that minimal cluster resources are consumed over time.
+        Note that this API does not support data streams.
       operationId: batch-start-upgrade-reindex
       requestBody:
         content:
@@ -43312,7 +43313,6 @@ paths:
       summary: Batch start or resume reindexing
       tags:
         - upgrade
-      x-state: Technical Preview
   /api/upgrade_assistant/reindex/batch/queue:
     get:
       description: |

x-pack/platform/plugins/private/upgrade_assistant/docs/openapi/upgrade_apis.yaml

@@ -259,8 +259,10 @@ paths:
       summary: Batch start or resume reindexing
       description: >
         Start or resume multiple reindexing tasks in one request.
-        Additionally, reindexing tasks started or resumed via the batch endpoint will be placed on a queue and run one-by-one, which ensures that minimal cluster resources are consumed over time.
-      x-state: Technical Preview
+        Additionally, [reindexing](https://www.elastic.co/docs/api/doc/kibana/operation/operation-start-upgrade-reindex) tasks for upgrading indices that are started or resumed via the batch endpoint will be placed on a queue and executed one-by-one.
+        This ensures that minimal cluster resources are consumed over time.
+
+        Note that this API does not support data streams.
       operationId: batch-start-upgrade-reindex
       tags:
         - upgrade