crypto: reduce retry delay when retrying KES requests (#10394)

This commit reduces the retry delay when retrying a request
to a KES server by:
 - reducing the max. jitter delay from 3s to 1.5s
 - skipping the random delay when there are more KES endpoints
   available.

If there are more KES endpoints we can directly retry to the request
by sending it to the next endpoint - as pointed out by @krishnasrinivas