[Internal]: Update Reporting memory requirements for PDF/PNG generation

### Description

The current documentation at https://www.elastic.co/docs/explore-analyze/report-and-share states:

> For Elastic Cloud Hosted deployments, Kibana instances require a minimum of 2GB RAM to generate PDF or PNG reports.

This is insufficient for larger or more complex dashboards. We've observed that PDF export of sample data dashboards (e.g., the Flights sample dashboard) fails with timeout or browser_screenshot_error("Target closed") on 2GB Kibana instances, while smaller dashboards export successfully. The headless Chromium process used for screenshotting runs out of memory on complex dashboards.

What needs to change:
- Update the 2GB minimum note to clarify that memory requirements scale with dashboard complexity and size.
- Recommend 4GB RAM for Kibana instances that generate reports for large or complex dashboards.
- Optionally mention the "Optimize for printing" (Print format) toggle as a workaround that reduces memory usage by capturing individual visualization snapshots instead of a single full-page screenshot.

Related issue: https://github.com/elastic/kibana/issues/250773

### Resources

- Slack discussion: https://elastic.slack.com/archives/CHSSGF015/p1773836667624479
- Related Kibana issue: https://github.com/elastic/kibana/issues/250773
- Current docs page: https://www.elastic.co/docs/explore-analyze/report-and-share

### Which documentation set does this change impact?

Elastic Cloud Hosted only

### Feature differences

N/A — this applies specifically to Elastic Cloud Hosted deployments where Kibana memory sizing is configurable.

### What release is this request related to?

9.2

### Serverless release

-

### Collaboration model

The engineering team

### Point of contact.

**Main contact:** @pmuellr

**Stakeholders:** @heespi, @tiamliu