[Draft] Clean interfaces for the imagine processes

[dbu]

Q	A
Branch?	3.x
Bug fix?	no
New feature?	no, but better names
BC breaks?	yes!
Deprecations?	no
Fixed tickets	#1413
License	MIT
Doc	TODO

Draft for clean interfaces as discussed at the Hackday at Liip.

We added the new interfaces and implementations under Domain to see what is new, but should move them to the root folder when things are ready.

Things that are missing in the draft

• Event system (do we want to keep it, do we need to change it?)
• Can we leverage the Config namespace somehow?
• One-shot transformations with a dynamic configuration

Will be done separatly in the refactor main branch after merging this branch:

• Adjust controller, commands and message handler to use the new interface #1593
• Refactor filters, post processors and flysystem to the new interfaces #1594
• Write ImageStore and ImageLoader with flysystem #1595