Support Mermaid icon pack registration for architecture diagrams

[kinghuang]

Mermaid's architecture-beta diagram type supports custom icons from Iconify via mermaid.registerIconPacks(). This allows diagrams to use service-specific icons (e.g., AWS S3, PostgreSQL, DuckDB) instead of only the five built-in icons (cloud, database, disk, internet, server).

Since Mintlify controls the Mermaid renderer, there's currently no way for users to register icon packs themselves. It would be great if Mintlify supported this — either by:

1. Pre-registering popular icon packs (e.g., logos, aws, simple-icons) so they're available out of the box, or
2. Allowing users to configure icon packs in docs.json, perhaps something like:

{
  "mermaid": {
    "iconPacks": [
      { "name": "logos", "url": "https://unpkg.com/@iconify-json/logos@1/icons.json" }
    ]
  }
}

Mermaid already supports a YAML frontmatter block for per-diagram configuration, so an alternative could be honoring icon registration there:

---
icons:
  - name: logos
    url: https://unpkg.com/@iconify-json/logos@1/icons.json
---
architecture-beta
  service s3(logos:aws-s3)[S3 Bucket]