Implement rate limit in nginx configuration

[Xpirix]

This is for #402 according to #402 (comment).

Change summary

• Apply a rate limit of 10 requests per second for each IP address

[timlinux]

Is it 10 per second or 10 per minute @Xpirix ?

[Xpirix]

@timlinux This PR proposes a rate limit of 10 requests per second for Nginx. This is for all requests including downloads.
The rate limit of 10 per minute is for the download only with the human validation as proposed in #405 (It also suggests 10 requests per second for Nginx).