Add SetExternalFrame function documentation

[Copilot]

This PR adds comprehensive documentation for the SetExternalFrame Drapo function, which enables communication with external iframe content by calling functions within the iframe and passing data from the current Drapo application context.

Changes Made

Documentation Structure

• Created /functions/SetExternalFrame/ directory following the established pattern
• Added description.html explaining the function's purpose
• Added parameters.json defining all 4 parameters with types and descriptions
• Created two working samples with complete HTML examples

Function Parameters

The SetExternalFrame function accepts 4 parameters:

1. FrameID - ID of the iframe element to communicate with
2. ExternalFunction - Name of function to call within the iframe
3. DataKey - Data key containing data to pass to the iframe
4. IsClone - Whether to clone the data before passing (optional, default: false)

Sample Examples

Sample 001: Basic iframe communication

<input type="button" value="Send Data to Frame" 
       d-on-click="SetExternalFrame(targetFrame,receiveUserData,userData,false)" />

Sample 002: Advanced data transfer with cloning options

<input type="button" value="Send Products (Cloned)" 
       d-on-click="SetExternalFrame(productFrame,displayProducts,productList,true)" />
<input type="button" value="Send Products (Reference)" 
       d-on-click="SetExternalFrame(productFrame,displayProducts,productList,false)" />

Verification

• ✅ Project builds successfully
• ✅ Application starts correctly
• ✅ Documentation structure matches existing function patterns
• ✅ All required files present with proper content

The SetExternalFrame function already exists in the Drapo framework but was missing from the documentation. This PR completes the documentation coverage for this important iframe communication feature.

Fixes #221.

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