feat(infra): Added way to run custom commands for different services

- new `EXTRA_FILES` docker build args to specify directory to be copied at
  /extra
- run `${SERVICE}/entrypoint.sh` as docker entry point
- added src/empty folder to so if EXTRA_FILES isn't set => use empty
  folder (since no conditional COPY)

src/.dockerignore

@@ -1,4 +1,5 @@
 **/node_modules
 **/dist
-@shared/src/database/init.sql.ts
 **/Dockerfile
+.gitkeep
+.dockerignore