Remove impress mentions from the codebase and docker images

[virgile-dev]

Bug Report

Problematic behavior
The project used to be called Impress. Now it's called Docs

Steps to Reproduce
There are a lot of places in the code where impress is mentionned.
The docker images are hence called impress-front-end and impress-backend.

Expected behavior/code
We should be consistent and only use docs as a project name.

Possible Solution

• Search and replace impress by docs in the code
• Create new images called Docs (no remane function docker, while pushing the history on this new name, no deletion of the impress images)

This will lead to breaking changes, it should be done at the same time and documented in a major release.