Merge pull request #38379 from Arhell/ja-doc

[ja] Document generating SHA256 CA certificate

Author: k8s-ci-robot

content/ja/docs/concepts/cluster-administration/certificates.md

@@ -105,7 +105,7 @@ weight: 20
 
         openssl x509 -req -in server.csr -CA ca.crt -CAkey ca.key \
         -CAcreateserial -out server.crt -days 10000 \
-        -extensions v3_ext -extfile csr.conf
+        -extensions v3_ext -extfile csr.conf -sha256
 1.  証明書を表示します。
 
         openssl x509  -noout -text -in ./server.crt