[elastic_agent]: Set `event.module` for all datasets in this integration

### Integration Name

Elastic Agent [elastic_agent]

### Dataset Name

All

### Integration Version

Latest

### Agent Version

Latest

### OS Version and Architecture

N/A

### User Goal

Many other integrations set the `event.module` field to indicate the integration name, especially when there are multiple datasets within an integration. User has alert rules setup based on the agent & module combination, though since this field is not populated, the alerts don't work the as as for other integrations. Ideal situation would be for `event.module` to be set to `elastic_agent` for all datasets within this integration.

### Existing Features

It possible to setup custom component templates, though as this integration has many data streams, it's a bit cumbersome to apply, and the current behavior is different from many other integrations that set a value out of the box.

### What did you see?

n/a

### Anything else?

This issue was raised by support on behalf of a customer.