this is necessary, since for Docker and electron-forge, we need to run this as an extra step after copy-dist
for electron-forge: after it is done with its own "pruning", as we otherwise would need to also take care of certain electron related pruning
for Docker: as a last step in the build stage
this will allow for cleaner separation -> build for the output from the build stage (i.e. TS/Webpack + asset copying) and dist for the archive format of the build folder
same changes as for the "non-alpine" Dockerfile previously commited, but adapted to Alpine.
this Dockerfile is aimed at production builds, i.e. trying to keep size as small as possible at the cost of "rebuild speed", due to missed docker cache opportunities.
Build Stage:
* do the complete build inside docker as oposed to the previous "hybrid", where tsc was run locally and the output got copied into the Docker build stage → you can now build this with Docker, without having to install the whole node/TS env locally
* build into a "build" subfolder, for easier clean up during build stage
* get rid of now unnecessary extra file/asset handling, as this is now handled by `npm run build:prepare-dist`
* no `npm prune` needed here, as we delete the whole build folder anyways in the last build step
Runtime stage:
* move the "electron" dep removal from the builder stage to the runtime stage, before installing the dependencies
* move to `npm ci` for reproducible installations – but only installing runtime deps here
* get rid of now unnecessary copying commands from the builder stage, as everything is now neatly available in "/usr/src/app"
