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