Enhance x-dropdown with Optional, Filterable, and Dynamic Capabilities

[wizardnet972]

Description:
Currently, the x-dropdown property in NX is used to define static dropdown options, for example:

"project": {
  "type": "string",
  "description": "The name of the project.",
  "aliases": ["p"],
  "x-dropdown": "projects"
},

I propose extending this functionality to support more advanced scenarios:

1. Optional Dropdown Configuration:
   Allow x-dropdown to be defined as an object rather than a static string. This change would enable more flexible usage and make it optional.

2. Filtering Projects:
   Introduce a filtering mechanism within x-dropdown to limit dropdown options based on criteria. For example:

   "project": {
     "type": "string",
     "description": "The name of the project.",
     "aliases": ["p"],
     "x-dropdown": {
       "$source": "projects",
       "filter": { "tag": "scope:...,type:..." }
     }
   }

3. Dynamic Dropdown Options:
   Support dynamic retrieval of dropdown options by allowing $source to reference a module function. For example:

   "x-dropdown": {
     "$source": "./tools/options.ts#getOptions"
   }

Benefits:

• Flexibility: Users can now customize and optionally apply dropdowns.
• Enhanced User Experience: Filtering will help narrow down large lists (e.g., in monorepos) based on tags or types.
• Dynamic Integration: Fetching options at runtime will allow integration with external data sources or custom logic.

I am happy to work on a pull request to implement these enhancements.