新增learn-kubernetes（https://github.com/yyong-brs/learn-kubernetes）相关文件

learn/learn-kubernetes-master/kiamol/ch17/docker-images/user-cert-generator/Dockerfile

@@ -0,0 +1,18 @@
+ARG ALPINE_VERSION="3.15"    
+FROM alpine:$ALPINE_VERSION
+
+RUN apk add --no-cache jq openssl
+RUN apk add --no-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing kubectl
+
+COPY start.sh /
+RUN chmod +x /start.sh
+
+ENV USER_NAME="reader@kiamol.net" \
+    GROUP="kiamol" \
+    SET_CONTEXT="" \
+    PRINT_CERTS=""
+
+WORKDIR /certs
+CMD /start.sh
+
+COPY csr.yaml .