Allow formulas to use a variable for the number of uploaded files

Currently, it is not possible to reference the number of uploaded files within formulas. It would be useful to introduce a variable that represents the total number of uploaded files, so this value can be used in pricing or calculation formulas.

Use case:
In situations where pricing or logic depends on how many files a user uploads, merchants should be able to include this value directly in their formula. For example, charging a fee per uploaded file or applying conditional logic based on the file count.

Proposed solution:
Introduce a variable (for example uploaded_files_count) that represents the total number of files uploaded by the user. This variable should be accessible within the formula builder and usable in calculations.

Example:
price = base_price + (uploaded_files_count * file_fee)

Expected outcome:
Merchants can dynamically calculate prices or apply logic based on the number of files uploaded, enabling more flexible configuration without custom development.