Survey Creator: Add a capability to select predefined "Maximum file sizes" in File Upload

[RomanTsukanov]

Convert this editor to a dropdown with support for entering a custom value:

Proposed predefined values:

Label	Value (in bytes)	Typical Use
100 KB	102400	Very small files (icons, text docs, thumbnails)
500 KB	512000	Small images or documents
1 MB	1048576	Standard office files or low-res photos
5 MB	5242880	Medium photos, short videos, PDFs
10 MB	10485760	Presentations, larger documents
25 MB	26214400	High-quality images, videos, large PDFs
50 MB	52428800	Video clips, multiple files zipped
100 MB	104857600	Heavy media uploads, datasets

[RomanTsukanov]

We need a dropdown that accepts custom values without saving them as a new choice option.

[tsv2013]

Probably we could implement a double-field editor with a value imput and a unit dropdown