refactor: Update perks for 2024 YEC; update perk-option selection copy in form

This MR performs two actions:

1. It updates the perks such that they match the intended YEC 2024 outlay of perks;
2. It updates the copy on the donation form to more properly indicate that the user must select a size (as at present, the presence of "perk options" is a 1:1 match to perks which come in "sizes").