Adding TAO headers to expose timing resource info

[marcelduran]

This PR adds Timing-Allow-Origin (TAO) header to images. This allows any origin to read resource timing values from the images. e.g.:

performance.getEntriesByType('resource').filter(e => e.name.includes('picsum'))[0].transferSize // should be > 0

[DMarby]

Hi @marcelduran,

Thank you for your contribution, sorry about the delay on getting this merged! This will be deployed shortly, but it may take a while until the header is present on all images, as the CDN cache will need to expire first, which generally takes around a month.