Increase nginx rate limit

[sync-by-unito]

Now nginx rate limiting from one IP is 7 requests per second (rate=7r/s, burst=10).
Skale-checks library (used by skale-supervisor and SLA monitoring) runs 13 checking threads in parallel, so the request limit should be increased at least to 13 r/s (better to 20)

┆Issue is synchronized with this Jira Task