Organize the folder hierarchy for dependencies

[dervoeti]

Decide where to place folders for Dockerfiles of dependencies and align the structure accordingly. Ensure each dependency has its own dedicated Dockerfile.

Currently preferred way:

• Dependencies used by only one specific product live in a subfolder of that product
• Dependencies used by multiple products live in a shared folder at the top level

Other ideas:

• All dependencies at the top level, next to our products
• All dependencies live in a separate dependencies subdirectory