[5.x] Add support for the 'PhotoSwipe Tiled Deep Zoom Plugin' as submodule

Yes this would be nice as submodule. If someone needs it, please start with a MR for a submodule.

I think it's a helpful, but kind of edge-case feature.

@thomas.frobieter: What do you think about the relevance of this feature for us? Would it help us a lot or possilby not very likely?

Not relevant to us in general, but for sure a nice feature, if you have something you need to look at in detail. Like .. I don't know.. construction plans, explosion drawings, etc.

So our team is not interested in implementing this, until we need it, but happy to review MR's! :)
This should be implemented as submodule to be optional.

I've made the sub-module to implement the plugin