CDPT-2264 Improve nginx's file serving.

[EarthlingDavey]

Previously a missing file caused an error. Now it's a 404 without an error.

Before:

[error] 30#30: *22939 open() "/var/www/html/public/app/themes/clarity/dist/globals/fonts/moji-clarity.ttf" failed (2: No such file or directory), client: 172.20.163.241, server: localhost, request: "GET /app/themes/clarity/dist/globals/fonts/moji-clarity.ttf?vklv4a HTTP/1.1", host: "intranet.justice.gov.uk", referrer: "https://intranet.justice.gov.uk/app/themes/clarity/dist/css/style.css?id=403678736ef4bf78b9131a99ad902082"

After:

172.21.0.8 - - [20/Nov/2024:16:19:12 +0000] "GET /app/themes/clarity/dist/globals/fonts/moji-clarity.ttf HTTP/1.1" 404 1375 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36" "192.168.65.1"