Which workspace a document is in, for a link that names no workspace

For an old link (`/sign/documents/<id>`, an email from before workspace URLs), so the app can send the tab to the same route under `/w/<slug>`. It works across the caller's workspaces: the token may be for any of them. It answers only when the caller could open the document in its own workspace: they are a member with a product seat, Sign is on there, and the document is theirs or shared with the workspace. Rows from before workspaces (no workspace) are not located. Every other case gets the same 404, byte for byte: no such document, someone else's private one, another workspace's, the product turned off there, a malformed id, or a request made with an API key or an OAuth grant (those are bound to one workspace by consent). Both answers are `Cache-Control: no-store`. Rate-limited per user and per client IP.

curl -X GET "https://example.com/v1/documents/string/locate"

{  "workspace_id": "0967198e-ec7b-4c6b-b4d3-f71244cadbe9",  "slug": "string"}