🐛 [#546] Fix cascade of requests firing

Hook dependencies operate on the identity, and the identity of
the selectedProducts changes every time on each render, while the
contents stay the same.

JSON.stringify is the recommended approach to mitigate using non-primivites
in hook dependency arrays.

Note that the caching masked the issue partially - it caused the
request cascade to stop, but the problem still showed with multi-
product appointments.

Backport-of: #569

src/components/appointments/ProductSelect.js

@@ -56,7 +56,8 @@ const ProductSelect = ({name, selectedProducts}) => {
   const {value} = getFieldProps(name);
   const getOptions = useCallback(
     async () => await getProducts(baseUrl, selectedProducts, value),
-    [baseUrl, selectedProducts, value]
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    [baseUrl, JSON.stringify(selectedProducts), value]
   );
   return (
     <AsyncSelectField