rocsp/config: fix PoolSize comment (#6110)

The go-redis docs say default is 10 * NumCPU, but the actual code says 5.

Extra context:

2465baaab5/options.go (L143-L145)

2465baaab5/cluster.go (L96-L98)

For Options, the default (documented) is 10 * NumCPUs. For ClusterOptions, the
default (undocumented) is 5 * NumCPUs. We use ClusterOptions. Also worth noting:
for ClusterOptions, the limit is per node.

rocsp/config/rocsp_config.go

@@ -53,7 +53,10 @@ type RedisConfig struct {
 	WriteTimeout cmd.ConfigDuration
 
 	// Maximum number of socket connections.
-	// Default is 10 connections per every CPU as reported by runtime.NumCPU.
+	// Default is 5 connections per every CPU as reported by runtime.NumCPU.
+	// If this is set to an explicit value, that's not multiplied by NumCPU.
+	// PoolSize applies per cluster node and not for the whole cluster.
+	// https://pkg.go.dev/github.com/go-redis/redis#ClusterOptions
 	PoolSize int
 	// Minimum number of idle connections which is useful when establishing
 	// new connection is slow.

test/config-next/ocsp-responder.json

@@ -11,6 +11,7 @@
         "10.33.33.7:4218"
       ],
       "timeout": "5s",
+      "poolSize": 100,
       "tls": {
         "caCertFile": "test/redis-tls/minica.pem",
         "certFile": "test/redis-tls/boulder/cert.pem",