docs: update query-key docs (#2214)

Author: TkDodo

docs/src/pages/guides/default-query-function.md

@@ -7,6 +7,7 @@ If you find yourself wishing for whatever reason that you could just share the s
 
 ```js
 // Define a default query function that will receive the query key
+// the queryKey is guaranteed to be an Array here
 const defaultQueryFn = async ({ queryKey }) => {
   const { data } = await axios.get(`https://jsonplaceholder.typicode.com${queryKey[0]}`);
   return data;

docs/src/pages/reference/useInfiniteQuery.md

@@ -27,9 +27,9 @@ The options for `useInfiniteQuery` are identical to the [`useQuery` hook](/refer
   - **Required, but only if no default query function has been defined** [`defaultQueryFn`](/guides/default-query-function)
   - The function that the query will use to request data.
   - Receives a `QueryFunctionContext` object with the following variables:
-    - `queryKey: QueryKey`
+    - `queryKey: EnsuredQueryKey`: the queryKey, guaranteed to be an Array
     - `pageParam: unknown | undefined`
-  - Must return a promise that will either resolves data or throws an error.
+  - Must return a promise that will either resolve data or throw an error.
   - Make sure you return the data *and* the `pageParam` if needed for use in the props below.
 - `getNextPageParam: (lastPage, allPages) => unknown | undefined`
   - When new data is received for this query, this function receives both the last page of the infinite list of data and the full array of all pages.

docs/src/pages/reference/useQuery.md

@@ -73,8 +73,8 @@ const result = useQuery({
   - **Required, but only if no default query function has been defined** See [Default Query Function](../guides/default-query-function) for more information.
   - The function that the query will use to request data.
   - Receives a `QueryFunctionContext` object with the following variables:
-    - `queryKey: QueryKey`
-  - Must return a promise that will either resolves data or throws an error.
+    - `queryKey: EnsuredQueryKey`: the queryKey, guaranteed to be an Array
+  - Must return a promise that will either resolve data or throw an error.
 - `enabled: boolean`
   - Set this to `false` to disable this query from automatically running.
   - Can be used for [Dependent Queries](../guides/dependent-queries).