Add config for caching of static assets

[amplifi]

Inconsistencies arising from obsolete static assets (particularly Javascript files) could result in errors for platform users or inaccurate content displays. Currently, our only way to resolve is to advise the user to clear their local browser cache and/or force refresh the page.

Implementing Cache-Control and ETags would help ensure users have the most recent versions of assets while allowing us to leverage browser caching more efficiently for improved performance.

[amplifi]

Done; follow up task to switch external static assets to internal hosting, so Inline Manual, js, etc will fall under these controls.