Fix permissions for npm scripts

[btlogy]

Part of #171

This PR should fix the permissions which were occurring because npm runs as node user regardless if anything else in the container runs as root!
The best option is to simply avoid the root as a best practice too.

But using a specific user/uid + group/gid usually requires some precautions as the current uid is not always 1000 (e.g.: GitHub runner).
The changes covers this with some build-arg which can be used to tune the uid and gid inside the image if needed (e.g.: GitHub workflows).

This PR also proposes a way to install the node modules in the parent directory where the module resolution mechanism will lookup up if they are not found in the current one (if the image is run alone).
Although, the whole idea to npm install the modules twice for the client image (once inside and once outside), but only once for the client-e2e one (outside) is questionable and should be improved separately (see related issue).

[btlogy]

The only possible reviewer is @piegamesde : would you have time for this?

[btlogy]

There is not enough maintainer around to review: merging (deployment is already broken after all).