[feature] Configure nginx to serve precompressed files (gzip/brotli)

[nemesifier]

Depends on openwisp/openwisp-utils#565 being resolved.

Let's update ansible-openwisp2 to remove the settings which turned off GZIP and BROTLI compression, also because they won't be valid anymore with the new package we're migrating to.

Let's then configure nginx to serve precompressed files (both gzip/brotli).