Allow custom fields in "Add Multiple" window

[Awey01]

Problem
The "Add Multiple" dialog in documents like Sales Invoice only shows predefined fields. This makes it impossible to include custom fields like item price, stock balance, or other specific data.

Proposed Solution
Allow users to configure the fields displayed in the "Add Multiple" dialog, including custom fields, via Customize Form or similar settings.

Alternative Suggestion
At least add more predefined fields (e.g., item rate, available quantity) to the "Add Multiple" dialog in Sales Invoice. Currently, the dialog looks too basic with just a single column for item names.

Why This is Needed
This feature would save time and improve flexibility for businesses that rely on additional fields for their workflows. For example, showing "Default Unit of Measure" or "Brand" directly in the dialog would significantly improve usability.

This enhancement would make ERPNext more user-friendly and adaptable to common use cases.

[Awey01]

Also, any advanced search in any doctype is very basic, and need customization