Merge branch 'cleanup-feature-proposal' into 'master'

Cleanup feature proposal template

## What does this MR do?

Changes the recommended template for feature proposals.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

I've been using the template for a while, and find that putting so many words into the h2 makes me think there's actual content there, until I realize I'm just reading the template text (again). I think we can get away with just putting `Description` as the header, and putting the suggested content for that section as plain text below for someone to replace.

## What are the relevant issue numbers?

## Screenshots (if relevant)

![image](/uploads/20a99c98a12aad84c1a7ec020f365b2f/image.png)

/cc @JobV 

See merge request !5240