chore: Refactors Destination calendar API endpoint with a bunch of fixes (#11789)

Co-authored-by: Omar López <zomars@me.com>

apps/api/lib/utils/extractUserIdsFromQuery.ts

@@ -0,0 +1,14 @@
+import type { NextApiRequest } from "next";
+
+import { HttpError } from "@calcom/lib/http-error";
+
+import { schemaQuerySingleOrMultipleUserIds } from "~/lib/validations/shared/queryUserId";
+
+export function extractUserIdsFromQuery({ isAdmin, query }: NextApiRequest) {
+  /** Guard: Only admins can query other users */
+  if (!isAdmin) {
+    throw new HttpError({ statusCode: 401, message: "ADMIN required" });
+  }
+  const { userId: userIdOrUserIds } = schemaQuerySingleOrMultipleUserIds.parse(query);
+  return Array.isArray(userIdOrUserIds) ? userIdOrUserIds : [userIdOrUserIds];
+}