Add customization for zoom levels in PhotoSwipe 5

[arnowelzel]

Also see:

https://wordpress.org/support/topic/is-there-a-way-to-change-the-initial-zoom-level/
https://wordpress.org/support/topic/smooth-zoom-does-not-work-on-pc/

For some users it may be helpful to customize the zoom levels for initial zoom and maximum manual zoom. These are two options passed to PhotoSwipe 5 on initialization and are fixed values at the moment.

To do:

• Add backend setting for initial zoom level, only available if PhotoSwipe 5 is selected
• Add backend setting for maximum zoom level, only available if PhotoSwipe 5 is selected
• Add passing the zoom settings to the frontend
• Add using the zoom settings for PhotoSwipe 5