Describe async behaviour of client libraries in page component README

The readme of the page component at https://github.com/adobe/aem-core-wcm-components/tree/main/content/src/content/jcr_root/apps/core/wcm/components/page/v3/page#loading-of-cssjs should be extended with a column explaining under which circumstances the according clientlib categories are loaded asynchronously (should describe both async and defer flag).

Open the page component README at content/src/content/jcr_root/apps/core/wcm/components/page/v3/page, starting at the Loading of CSS/JS section linked in the issue. Extend the clientlib categories table with a column describing when loading is asynchronous, covering both async and defer; done means the README documents both flags and their circumstances.

Written by the indexing model from the issue text.