Feature Request: Add enum/dropdown support for user_config fields

[EfriNS]

Problem

Currently, MCPB 0.3 user_config only supports primitive types: string, number, boolean, directory, file. This limits configuration UX when extensions need users to select from a predefined set of options.

Use Case (Anonymized)

A monitoring extension tracks various SaaS platforms. The extension has pre-built scrapers for certain platforms (e.g., Platform A, Platform B, Platform C) with rich data sources, while unsupported platforms fall back to basic RSS scraping.

Current workaround:

"user_config": {
  "platforms": {
    "type": "string",
    "description": "Comma-separated list: PlatformA, PlatformB, PlatformC",
    "default": "PlatformA, PlatformB"
  }
}

Problems with this approach:

• Users can enter unsupported platform names → silent failures or degraded experience
• No validation at configuration time
• Unclear which platforms are fully supported vs experimental
• Poor UX (manual typing vs dropdown selection)

Proposed Solution

Add enum type support for user_config:

"user_config": {
  "platforms": {
    "type": "enum",
    "title": "Platforms to Monitor",
    "options": ["PlatformA", "PlatformB", "PlatformC"],
    "multiple": true,
    "default": ["PlatformA", "PlatformB"],
    "required": false
  }
}

UI behavior:

• Renders as dropdown (single) or multi-select (when multiple: true)
• Validates at configuration time
• Clear set of supported values

Alternative Syntax

Could also extend existing string type:

"platforms": {
  "type": "string",
  "enum": ["PlatformA", "PlatformB", "PlatformC"],
  "multiple": true
}

Benefits

1. Prevents user errors - No typos or unsupported values
2. Better UX - Dropdown selection vs manual typing
3. Clear expectations - Users see exactly what's supported
4. Validation - Errors caught at config time, not runtime

Related

Similar to how directory and file types provide specialized UI (file pickers), enum would provide specialized UI (dropdowns/multi-select).