build: consider compressing served static files

[mdonadoni]

After adding jsroot to preview ROOT files, JS source files have gotten bigger, see https://github.com/reanahub/reana-ui/pull/326#issuecomment-1564485956. This might get worse in the future when new dependencies will be added to the project.

In that same PR, we have already implemented lazy loading to avoid loading jsroot when not necessary. However, we should also consider compressing static files before serving them:

• check which format to use (depending on popularity, browser support, server side support, performance, ...)
• decide whether it's worth it to enable compression
• start serving compressed static files (JS sources, but also CSS), either:
  • compressed on-the-fly at runtime (see NGINX docs about compression)
  • generating already compressed sources at build-time and serving them (see gzip_static directive of NGINX as an example)