[9.1] [UII] Remove system-managed properties (dates) when updating index templates (#231524) (#232160)

# Backport

This will backport the following commits from `main` to `9.1`:
- [[UII] Remove system-managed properties (dates) when updating index
templates (#231524)](#231524)

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

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

<!--BACKPORT [{"author":{"name":"Jen
Huang","email":"[email protected]"},"sourceCommit":{"committedDate":"2025-08-13T19:23:04Z","message":"[UII]
Remove system-managed properties (dates) when updating index templates
(#231524)\n\n## Summary\n\nResolves #230902. This PR removes
system-managed properties (dates) from\nthe retrieved index templates
when updating the same index template\n(triggered when experimental
datastream feature settings have been\nchanged). The test that was
failing is now re-enabled.\n\nSimilar to
#231505, this is due to\nES
introducing these new date/timestamp fields
in\nhttps://github.com/elastic/elasticsearch/pull/131536.","sha":"9cdbe77e42ef8985daaf719da7c9895c6a56444d","branchLabelMapping":{"^v9.2.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","Team:Fleet","backport:version","v9.2.0","v9.1.3","v8.19.3","v9.0.6"],"title":"[UII]
Remove system-managed properties (dates) when updating index
templates","number":231524,"url":"https://github.com/elastic/kibana/pull/231524","mergeCommit":{"message":"[UII]
Remove system-managed properties (dates) when updating index templates
(#231524)\n\n## Summary\n\nResolves #230902. This PR removes
system-managed properties (dates) from\nthe retrieved index templates
when updating the same index template\n(triggered when experimental
datastream feature settings have been\nchanged). The test that was
failing is now re-enabled.\n\nSimilar to
#231505, this is due to\nES
introducing these new date/timestamp fields
in\nhttps://github.com/elastic/elasticsearch/pull/131536.","sha":"9cdbe77e42ef8985daaf719da7c9895c6a56444d"}},"sourceBranch":"main","suggestedTargetBranches":["9.1","8.19","9.0"],"targetPullRequestStates":[{"branch":"main","label":"v9.2.0","branchLabelMappingKey":"^v9.2.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/231524","number":231524,"mergeCommit":{"message":"[UII]
Remove system-managed properties (dates) when updating index templates
(#231524)\n\n## Summary\n\nResolves #230902. This PR removes
system-managed properties (dates) from\nthe retrieved index templates
when updating the same index template\n(triggered when experimental
datastream feature settings have been\nchanged). The test that was
failing is now re-enabled.\n\nSimilar to
#231505, this is due to\nES
introducing these new date/timestamp fields
in\nhttps://github.com/elastic/elasticsearch/pull/131536.","sha":"9cdbe77e42ef8985daaf719da7c9895c6a56444d"}},{"branch":"9.1","label":"v9.1.3","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"8.19","label":"v8.19.3","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"9.0","label":"v9.0.6","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: Jen Huang <[email protected]>

Author: kibanamachine

x-pack/platform/plugins/shared/fleet/common/types/models/epm.ts

@@ -763,6 +763,13 @@ export interface IndexTemplate {
   composed_of: string[];
   ignore_missing_component_templates?: string[];
   _meta: object;
+
+  // These properties are returned on ES read operations and
+  // not allowed to be set on ES write operations
+  created_date?: number;
+  created_date_millis?: number;
+  modified_date?: number;
+  modified_date_millis?: number;
 }
 
 export interface ESAssetMetadata {

x-pack/platform/plugins/shared/fleet/server/services/package_policies/experimental_datastream_features.ts

@@ -199,8 +199,17 @@ export async function handleExperimentalDatastreamFeatureOptIn({
       });
     }
 
-    const indexTemplate = indexTemplateRes.index_templates[0].index_template;
-    let updatedIndexTemplate = indexTemplate as IndexTemplate;
+    const rawIndexTemplate = indexTemplateRes.index_templates[0].index_template;
+
+    // Remove system-managed properties (dates) that cannot be set during create/update of index templates
+    const {
+      created_date: createdDate,
+      created_date_millis: createdDateMillis,
+      modified_date: modifiedDate,
+      modified_date_millis: modifiedDateMillis,
+      ...indexTemplate
+    } = rawIndexTemplate as IndexTemplate;
+    let updatedIndexTemplate = indexTemplate;
 
     if (isTSDBOptInChanged) {
       const indexTemplateBody = {