Fix typo and formatting in data stream scenario (#4009)

This PR:

- fixes some typos (`datastreams` -> `data streams` & `Policy` ->
`policy`) in the warning admonition
- fixes the list formatting in the warning admonition to use `*` instead
of a mixed `-` and `+`
- fixes the `json` code example’s indentation in the numbered list.

Previously, the `json` code example’s indentation caused the Github diff
view to highlight a large amount of text as containing an error.

Before:

<img width="1101" height="740" alt="Screenshot 2025-11-20 at 10 32 19"
src="https://github.com/user-attachments/assets/7d12b77f-71de-42ba-9dfb-86b8da9c1d09"
/>

After:

<img width="939" height="835" alt="Screenshot 2025-11-20 at 12 03 02"
src="https://github.com/user-attachments/assets/77a2f6b8-6f1a-4464-953b-871b93939066"
/>

Author: vishaangelova

reference/fleet/data-streams-scenario3.md

@@ -56,13 +56,13 @@ metrics-system.network-production@custom
 3. Use the template above to set the name—in this case, `metrics-system.network-production@custom`. Click **Next**.
 4. Under **Index settings**, set the {{ilm-init}} policy name under the `lifecycle.name` key:
 
-    ```json
-    {
-      "lifecycle": {
-        "name": "90-days-default"
-      }
-    }
-    ```
+   ```json
+   {
+     "lifecycle": {
+       "name": "90-days-default"
+     }
+   }
+   ```
 
 5. Continue to **Review** and ensure your request looks similar to the image below. If it does, click **Create component template**.
 
@@ -78,10 +78,9 @@ metrics-system.network-production@custom
 Now that you’ve created a component template, you need to create an index template to apply the changes to the correct data stream. The easiest way to do this is to duplicate and modify the integration’s existing index template.
 
 ::::{warning}
-- If you duplicate an index template, do not change or remove any managed properties. This may result in problems when upgrading. Cloning the index template of an integration package involves some risk as any changes made to the original index template are not propagated to the cloned version when you upgrade versions. 
-- These steps assume that you want to have a namespace specific ILM policy, which requires index template cloning. Cloning the index template of an integration package involves some risk because any changes made to the original index template as part of package upgrades are not propagated to the cloned version. Check out [Cloning the index template of an integration package](/reference/fleet/integrations-assets-best-practices.md#assets-restrictions-cloning-index-template) for details.
-
-+ If you want to change the ILM Policy, the number of shards, or other settings for the datastreams of one or more integrations, but **the changes do not need to be specific to a given namespace**, use a `@custom` component template, as described in [Scenario 1](/reference/fleet/data-streams-scenario1.md) and [Scenario 2](/reference/fleet/data-streams-scenario2.md), to avoid the problems mentioned earlier. Check out the [ILM](/reference/fleet/data-streams.md#data-streams-ilm) section for details.
+* If you duplicate an index template, do not change or remove any managed properties. This may result in problems when upgrading. Cloning the index template of an integration package involves some risk as any changes made to the original index template are not propagated to the cloned version when you upgrade versions. 
+* These steps assume that you want to have a namespace specific ILM policy, which requires index template cloning. Cloning the index template of an integration package involves some risk because any changes made to the original index template as part of package upgrades are not propagated to the cloned version. Check out [Cloning the index template of an integration package](/reference/fleet/integrations-assets-best-practices.md#assets-restrictions-cloning-index-template) for details.
+* If you want to change the ILM policy, the number of shards, or other settings for the data streams of one or more integrations, but **the changes do not need to be specific to a given namespace**, use a `@custom` component template, as described in [Scenario 1](/reference/fleet/data-streams-scenario1.md) and [Scenario 2](/reference/fleet/data-streams-scenario2.md), to avoid the problems mentioned earlier. Check out the [ILM](/reference/fleet/data-streams.md#data-streams-ilm) section for details.
 
 ::::