(core) provide a way for an administrator to force reload of a document

Summary:
Adds POST /api/housekeeping/docs/:docId/force-reload, which allows the support user to force a document to reload (even if they don't otherwise have access to the document).

This could be done without a separate endpoint, but that turned out a bit messy, and there's some advantage to quarantining the exceptional authorization somewhere it could be easily elaborated.

Test Plan: adds test

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2713

app/gen-server/lib/Housekeeper.ts

@@ -151,6 +151,16 @@ export class Housekeeper {
         headers,
       });
     }));
+
+    // Force a document to reload.  Can be useful during administrative
+    // actions.
+    app.post('/api/housekeeping/docs/:docId/force-reload', this._withSupport(async (docId, headers) => {
+      const url = await this._server.getHomeUrlByDocId(docId, `/api/docs/${docId}/force-reload`);
+      return fetch(url, {
+        method: 'POST',
+        headers,
+      });
+    }));
   }
 
   /**