Add new achievement UI

What does this MR do and why?

Add new achievement UI

Changelog: added

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screen_Recording_2024-03-04_at_21.22.32

How to set up and validate locally

1. Enable the achievements feature flag in the rails console: Feature.enable(:achievements)
2. Visit the achievements page for a group (there's no nav menu item, you'll need to navigate by entering the URL directly): http://gdk.test:3000/groups/flightjs/-/achievements/
3. Select Add achievement
4. Try adding an achievement with a unique name (it should appear at the bottom of the list)
5. Try adding an achievement with an existing name (it should return an error)

Related to #390407