Make private source maps easily available for sentry and developers

[keskiju]

Currently you can copy source maps from running container to your local disk (taito copy from:client:prod /meta ./tmp/meta) and then use them in browser dev tools. This is a bit awkward, and not even possible if you don't have access to production container. Also Sentry requires access to source maps.

We should publish source maps in some private location. Some ideas: https://itnext.io/using-sourcemaps-on-production-without-revealing-the-source-code-%EF%B8%8F-d41e78e20c89