fix(overlay): correct parameter name from 'positioningStrategy' to 'positionStrategy' in documentation

[norikois]

Summary

This PR fixes the API link position for the PositionStrategy reference used in the Overlay documentation.

What changed

• Adjusted the API link to positionStrategy member in OverlaySettings

Before
<ApiLink kind="interface" type="OverlaySettings" member="positioningStrategy" />

After¨
<ApiLink kind="interface" type="OverlaySettings" member="positionStrategy" />

Impact

• Documentation-only change.

Verification

• Confirmed the Overlay doc page now shows the PositionStrategy API link.
• Checked and confirmed by running npm run check-mdx-links:angular in the local repo.

Closes # N/A

Checklist:

• check topic's TOC/menu and paragraph headings
• Include TOC topic labels in the topic content when it has a valuable update, is new, or is considered preview / beta
• link to other topics using ./page.mdx or ../relative/path.mdx (.mdx extension required)
• at the References section at the end of the topic add links to topics, samples, etc
• reference API documentation instead of adding a section with API

• use valid component names - [Data] Grid, IgxSelectComponent, <igx-combo>
• use spell checker tool (VS Code, Grammarly, Microsoft Editor)
• add inline code blocks for the names of classes / tags / properties
• add language descriptor for the code blocks
• check if links function by running the check-api/mdx npm commands
• check if sample is working and fully visible in the topic
• check if sample is working and fully visible in the StackBlitz
• check if code blocks match the code in StackBlitz demo
• add or update meaningful llms.description metadata and run npm run check:llms-metadata

• follow SEO guidelines to fill topic's metadata (SEO guidelines)

• do not resolve requested changes (leave that to the reviewer)