Export source maps when building a release of app-frontend

[olemartinorg]

With source-maps it becomes much easier to trace errors that may happen in finished builds, and even though the source map is quite large, it won't be downloaded unless you open the browser DevTools.

Now that the CDN doesn't have the storage issues it once had, this should be obtainable.

Related issues

• https://altinndevops.slack.com/archives/C045EB3JA9X/p1706626290839569?thread_ts=1706620520.707779&cid=C045EB3JA9X
• Enabling redux devtools in production #465