Update GSoC ideas template to include difficulty rating

[nate-double-u]

Required elements (these we already have)

a) a project title/description b) more detailed description of the project (2-5 sentences) c) expected outcomes d) skills required/preferred e) possible mentors f) expected size of project (90, 175 or 350 hour – yes, 3 options starting in 2024).

Optional element

And if possible, an easy, intermediate or hard/difficult rating of each project. This helps the more inexperienced folks not get overwhelmed and they can focus on reviewing easy project ideas.