Minimize Documentation template

What does this MR do?

In an effort to simplify and streamline MR creation, this MR attempts to minimize the amount of content contained in the Documentation template for merge request creation. This builds off of observations that many users don't select a majority of the tasks as being completed. It also surfaces the most important items for Documentation MRs (reviews, guidelines, the Style Guide, and label usage). All other items can be discovered from those links.