Add a "fetchpriority" property to the API

[jobee]

Since priority hints are now shipped for chromium-based browsers, I suggest to extend the API by adding a fetchpriority property.

see https://web.dev/priority-hints/

Or would you recommend adding the fetchpriority attribute like

<Sitegeist.Kaleidoscope:Image
    ...
    attributes.fetchpriority="high"
/>

...?

[manuelmeister]

I think adding it with attributes is the correct way.