Moving quick actions, shortcuts, markdown to Manage your code

The "Plan and track work" section is about scrum, setting up issue boards, and prepping your work.

The "Manage your code" section is about doing the work. About coding features and checking them in.

I think these features make the most sense when you are working in the product, rather than when you are planning your sprints.

Related to: gitlab#448619 (closed)