Set up bundle cache for ruby gems

[stringiest]

Try instructions in these five posts to set up cache service in docker-compose.yml: 1 - https://stackoverflow.com/questions/49032151/docker-compose-rebuild-after-each-gemfile-update 2 - https://stackoverflow.com/questions/70616142/how-to-use-bundler-cache-to-speed-up-bundle-install 3 - https://stackoverflow.com/questions/52921426/docker-compose-version-3-cache-gems-to-speed-up-run-time-bundle-install 4 - https://dev.to/yourivdlans/dependency-manager-cache-with-docker-build-33mh 5 - https://bradgessler.com/articles/docker-bundler/