Add `system#remark` to referenda templates

[wliyongfeng]

In WishForChange track, communities propose system#remark call. We can add this template to referenda templates to help users with this process.

@Popoulosss We need a simple design for this issue.

[Popoulosss]

• Add a Remark proposal item to quick start
• The default track option is [2] Wish For Change
• The default input format is markdown

Figma link

Preview