Resolve "Promote Issue weight"

What does this MR do?

It promotes Issue Weight, so now the weight display is always activated and if you click on Edit and you are not having that feature in your instance/plan then we show a promotion. The basic rules of how and what to show for promotions were already established & extensively reviewed here : gitlab-org/gitlab-ee!2540 This MR is following and applying the same patterns here.

Why was this MR needed?

To promote our awesome EE features to all the people who don't have them yet.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #2946 (closed)