Super sidebar: New grouping for groups menu

What does this MR do and why?

Refactor how we pick menus into a panel

Picking items manually is a little tricky, if we consider a CE/EE split. It just seems easier if a menu defines itself, whether it should be picked into the SuperSidebarPanel.

Super sidebar: New grouping for groups menu

Group menu items for groups and subgroups.

See #378546 (closed)

Super sidebar: Test whether group items are serializable

This adds a shared test behavior for menus, to test whether they are serializable as menu_items: serializable as super_sidebar_menu_args.

And another one for menus that are not serializable: not serializable as super_sidebar_menu_args

Furthermore we enforce that serializable items should define an item_id.

And we have a minor fix and add the active_route to the Issues menu.

Super sidebar: Properly test serializable menus

This increases our test coverage on the projects sidebar as well.

Screenshots or screen recordings

Before	After

• As you can see, menu-items from "Group Information", "Epics", "Issues" and "Wiki" have been merged into the "Plan" menu.
• The "Operations" Menu mainly consists of "Packages and registries"
• Epic > Boards and Issue > Boards have been renamed to "Plan > Epic boards" and "Plan > Issue boards". Apart from that nothing was renamed (yet), and we only focused on the structure of the menu. There will be follow-up MRs to rename the items as part of #378546 (closed) and also adjust the styling.

How to set up and validate locally

1. Enable the super_sidebar_nav feature flag.
2. Log into the GDK and enable the New Navigation for the current user via the User Menu
3. Go to any group

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.