[Automatic Import] Add datastream name as dataset value in manifest (#…

…203106)

## Release note

Use Data stream name for data_stream.dataset value in input manifests

## Summary

Closes #201478

This PR uses the user-supplied data stream name as the
`data_stream.dataset` value instead of a generic placeholder.

Custom Fleet integrations default to a generic dataset
(data_stream.dataset) value - something like `http_endpoint.generic.`
Since users configure their own options for a custom integration, this
workflow makes sense.

Elastic integrations, on the other hand, default to a predetermined
naming convention based on the integration package + datastream name for
dataset - something like github.issues for the issues data stream from
the Github package.

Hence defaulting it to `package_name.datastream_name`

<img width="729" alt="Screenshot 2024-12-05 at 15 12 32"
src="https://github.com/user-attachments/assets/2dad5de3-a329-403f-be46-2dbc76906b03">


<img width="868" alt="Screenshot 2024-12-05 at 15 12 16"
src="https://github.com/user-attachments/assets/2959e26a-8095-4efa-bf9b-c5e953e849b9">



### Checklist

Check the PR satisfies following conditions. 

- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/plugins/integration_assistant/server/templates/manifest/cel_manifest.yml.njk

@@ -10,7 +10,8 @@
       title: Dataset name
       description: |
         Dataset to write data to. Changing the dataset will send the data to a different index. You can't use `-` in the name of a dataset and only valid characters for [Elasticsearch index names](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-index_.html).
-      default: cel.cel
+      default: |
+        {{ package_name }}.{{ data_stream_name }}
       required: true
       show_user: true
     - name: pipeline

x-pack/plugins/integration_assistant/server/templates/manifest/http_endpoint_manifest.yml.njk

@@ -32,7 +32,8 @@
       title: Dataset name
       description: |
         Dataset to write data to. Changing the dataset will send the data to a different index. You can't use `-` in the name of a dataset and only valid characters for [Elasticsearch index names](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-index_.html).
-      default: http_endpoint.generic
+      default: |
+        {{ package_name }}.{{ data_stream_name }}
       required: true
       show_user: true
     - name: pipeline

x-pack/plugins/integration_assistant/server/templates/manifest/kafka_manifest.yml.njk

@@ -26,7 +26,8 @@
       title: Dataset name
       description: |
         Dataset to write data to. Changing the dataset will send the data to a different index. You can't use `-` in the name of a dataset and only valid characters for [Elasticsearch index names](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-index_.html).
-      default: kafka_log.generic
+      default: |
+        {{ package_name }}.{{ data_stream_name }}
       required: true
       show_user: true
     - name: pipeline