feat: client Dockerfile - added comments so we understand what is happening and why, fix: corrected copying of package-lock.json

feat: docker-compose - added mapping of package*.json files from the host to the container, added comments describing what is happening and why

fix: docker-compose - renamed client env variable SERVER_PORT to VITE_SERVER_PORT so VITE can access it

feat: docker-compose - created frontend network for client and nginx, deleted env_file in client for safety reasons

fix: vite/react client port is specified in .env file and it applies everywhere - it's not hard-coded anymore

fix: nestjs server port is specified .env file and it applies everywhere - it's not hard-coded anymore

fix: added adminer back to the same network as other backend stuff because otherwise it doesn't see database

feat: added to Docker - Postgres db and Adminer db manager, added .env-example as hint for local .env file