(NII-Proposal) feat(files): add dynamic file provider registry for foreign addon support

[chiku-samugari]

Purpose

The Files route /{guid}/files/{provider} is guarded by isFileProvider, which admits only the provider
names listed in the build-time constant FileProvider. A storage service that GravyValet serves under any
other name cannot be opened: the route does not match, the router falls through to the file-detail route,
and the page shows an empty file view for a file that does not exist.

GravyValet PR #318 (Foreign Addon Imps)
lets a deployment add storage add-on implementations as external packages. Such a service is registered in
GravyValet, served by osf.io and WaterButler, listed on the Add-ons page, and browsable in the files
widget of the project overview, but the Files page refuses its name. This PR extends that last build-time allow-list.

Summary of Changes

• Add FileProviderRegistryService, the registry of valid provider names.
  • The built-in FileProvider values are known from the start and are answered without any request.
  • The first time the registry is asked for a name it does not know, it fetches the
    external_service_name of every service returned by GravyValet's GET /v1/external-storage-services
    and keeps the result until the page is reloaded.
  • While the request is pending, the full-screen loader is shown, as ResourceService.getResourceById
    does for the resource lookup of the :id guards.
• Make isFileProvider ask the registry asynchronously instead of the build-time list.
• Introduce a new type FileProviderType for the provider field of the files state.
  The type states what the field holds with this PR: a built-in name, or a name that GravyValet lists.
• Fall back to the name served by GravyValet for a service that the AddonServiceNames enum does not list.
  This avoids an empty name in the success toasts and in the header of the disconnect dialog.
• Tests
  • Add new specs for the registry and AddonDialogService
  • Rewrite spec for the guard
  • Revive specs of ConnectConfiguredAddonComponent and ConnectAddonComponent that cover
    the create and update flows and the name in the success toast.

Screenshot(s)

n/a

Side Effects

• The Files route now depends on GravyValet for names that are not built-in. Opening
  /{guid}/files/{name} with a name other than the built-in providers sends one request to GravyValet
  (GET /v1/external-storage-services) before the route is matched, once per page load. This includes
  the file-detail URLs /{guid}/files/{fileGuid}, which share the route prefix and do not use GravyValet
  today.
• The provider of the files state can now be a name that FileProvider does not list. The type
  allowed this before (it resolved to string), so this is a change of the values at run time, not of the
  types.

QA Notes

• Pages: Files page of a project and of a registration; project overview files widget; move/copy dialog.
• Cases:
  • a built-in provider (/{guid}/files/osfstorage, /{guid}/files/googledrive) opens as before;
  • with a foreign storage add-on configured on the project, /{guid}/files/<name> opens, including on a
    direct page load and reload;
  • an unknown file provider name (/{guid}/files/nope) is still rejected;
  • logged-out visitor on a public project: Files page works;
  • a file-detail page (/{guid}/files/{fileGuid}) opens as before.
• Add-on names (project Add-ons page and user settings Add-ons page):
  • storage service that uses froeign addon imp: the disconnect dialog header and the success toast after
    connecting show the service's name instead of an empty one;
  • built-in service: the texts are not changed.
• Risk: low. The guard becomes permissive only for names GravyValet lists.
• Cross-browser testing: not required.
• Requires a GravyValet that includes PR #318,
  with at least one foreign storage add-on registered.