Request to complement Fleet Docs "Tutorial: Transform data with custom ingest pipelines" with information in KB article

### Description

The following documentation https://www.elastic.co/docs/reference/fleet/data-streams-pipeline-tutorial, has instructions on how to add a custom pipeline to an integration by calling it from the default ingest pipeline.

The step "[Edit integration](https://www.elastic.co/docs/reference/fleet/data-streams-pipeline-tutorial#_edit_integration)" mentions what needs to be done for that:
> The integration must already be configured and installed before a custom pipeline can be added. To enter this workflow, do the following:
> 1. Navigate to Fleet
> 2. Select the relevant Elastic Agent policy
> 3. Search for the integration you want to edit
> 4. Select Actions → Edit integration

But while doing that, there a few things happening with the integration assets and UI that are not reflected in the documentation which is creating confusion on how this setting flow works amongst my peers. For reference, Slack Thread when the suggestion to create a docs ER came up (Elastic internal): https://elastic.slack.com/archives/C047UAW6JG5/p1757618054615929

I created the following KB article to complement this content: [Clarifications on how to add and manage Ingest Pipelines for Elastic Integrations](https://support.elastic.dev/knowledge/view/ac796f3b)

Could the documentation be complemented with the content in the KB article so it's easier to follow and know what the configuration should look like?

### Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

### Feature differences

The feature is identical for all deployment methods.

### What release is this request related to?

N/A

### Serverless release

Unknown.

### Collaboration model

The product team.

### Point of contact.

**Main contact:** @

**Stakeholders:**