Chore/allow collections move

[seaerchin]

Problem

previously we disallowed users from shifting items inside collections. this pr allows shifting of collection items between collections.

1. this means that collection items can only be moved between collections and not into folders
2. similarly, folder items can only be moved between folders and not into collections

Solution

1. fetch data using getChildrenOf and filter
2. show the menu tooltip on collection items
3. this is a frontend only change - the backend method will still allow users if they post directly and are verified

Tests

1. create 2 collections
2. create a folder
3. create pages inside the collections + the folder
4. create links inside the collections
5. for the page inside the folder, verify that you cannot move it to another collection
6. for the pages inside the collection + the link, verify that you can move them between collections
7. verify that the pages + link once moved, doesnt show inside the original collectino both on the dashboard and the sidebar
8. verify that the pages + link once moved, shows inside the new collection on the sidebar + the dashboard

[datadog-opengovsg]

Datadog Report

Branch report: chore/allow-collections-move
Commit report: 72cae15
Test service: isomer-studio

✅ 0 Failed, 257 Passed, 36 Skipped, 44.97s Total Time
➡️ Test Sessions change in coverage: 1 no change

[dcshzj]

nit: I think I've seen this if-else a couple of times, might be good to standardise to use a common function that determines the icon to use

For example, ICON_MAPPINGS inside apps/studio/src/features/dashboard/components/DirectorySidebar/constants.ts has this mapping for all the resources currently.

[dcshzj]

issue(perf): I think we should still continue using getFolderChildrenOf, otherwise it seems a bit heavy for the client browser to perform the filtering on the entire list of resources, rather than letting the backend perform an initial filtering to folder-like resources.

[dcshzj]

nit: might be good to add a comment about the frontend-side filtering, which makes moving items from Folder to Collection (and vice versa) not possible to a normal user.