Configure platform contexts for ApiLink index resolution

[viktorkombov]

Summary

Adds ApiLink index configuration to platform contexts so docs can resolve API links through the generated api-docs registry.

This keeps MDX usage simple and avoids repeating pkg, kind, prefix, and suffix details in content files.

Changes

• Added apiLinkIndexRoot to platform contexts.
• Added API docs base URL handling for staging, production, and local api-docs testing.
• Keeps local testing configurable through API_DOCS_BASE_URL.
• Preserves existing ApiLink fallback behavior when the index is unavailable.

Testing

Run api-docs locally:
npm run start:angular:en -- --port 4322

Run docs-template against it:
$env:API_DOCS_BASE_URL="http://localhost:4322/api"
npm run angular:dev

Verify Angular dashboard tile API links:

• CategoryChart resolves to igniteui-angular-charts
• DataChart resolves to igniteui-angular-charts
• GeographicMap resolves to igniteui-angular-maps
• member links resolve with anchors
• excluded links still render as code on excluded platforms