fix: update base image to maven supported (OpenAPITools#7001)

* Updates docker images for CLI and Online to JDK 11 and Maven 3.6.3 builders
* Uses openjdk:11.0.8-jre-slim-buster rather than alpine as new image publishes CVEs

.hub.cli.dockerfile

@@ -3,10 +3,7 @@
 ##
 ## You can build _just_ this part with:
 ##     docker --target builder -t container-name:builder -f .hub.cli.dockerfile .
-FROM jimschubert/8-jdk-alpine-mvn:1.0 as builder
-
-RUN set -x && \
-    apk add --no-cache bash
+FROM maven:3.6.3-jdk-11-openj9 as builder
 
 ENV GEN_DIR /opt/openapi-generator
 WORKDIR ${GEN_DIR}
@@ -18,11 +15,10 @@ RUN mvn -am -pl "modules/openapi-generator-cli" package
 ## The final (release) image
 ## The resulting container here only needs the target jar
 ## and ca-certificates (to be able to query HTTPS hosted specs)
-FROM openjdk:8-jre-alpine
+FROM openjdk:11.0.8-jre-slim-buster
 
 ENV GEN_DIR /opt/openapi-generator
 
-RUN apk --no-cache add ca-certificates bash
 RUN mkdir -p ${GEN_DIR}/modules/openapi-generator-cli/target
 
 WORKDIR ${GEN_DIR}/modules/openapi-generator-cli/target

.hub.online.dockerfile

@@ -3,10 +3,7 @@
 ##
 ## You can build _just_ this part with:
 ##     docker --target builder -t container-name:builder -f .hub.online.dockerfile .
-FROM jimschubert/8-jdk-alpine-mvn:1.0 as builder
-
-RUN set -x && \
-    apk add --no-cache bash
+FROM maven:3.6.3-jdk-11-openj9 as builder
 
 ENV GEN_DIR /opt/openapi-generator
 WORKDIR ${GEN_DIR}
@@ -17,7 +14,7 @@ RUN mvn -am -pl "modules/openapi-generator-online" package
 
 ## The final (release) image
 ## The resulting container here only needs the target jar
-FROM openjdk:8-jre-alpine
+FROM openjdk:11.0.8-jre-slim-buster
 
 ENV GEN_DIR /opt/openapi-generator
 ENV TARGET_DIR /generator

Dockerfile

@@ -1,7 +1,4 @@
-FROM jimschubert/8-jdk-alpine-mvn:1.0
-
-RUN set -x && \
-    apk add --no-cache bash
+FROM maven:3.6.3-jdk-11-openj9
 
 ENV GEN_DIR /opt/openapi-generator
 WORKDIR ${GEN_DIR}
@@ -29,6 +26,6 @@ RUN mvn -am -pl "modules/openapi-generator-cli" package
 COPY docker-entrypoint.sh /usr/local/bin/
 RUN ln -s /usr/local/bin/docker-entrypoint.sh /usr/local/bin/openapi-generator
 
-ENTRYPOINT ["docker-entrypoint.sh"]
+ENTRYPOINT ["/usr/local/bin/docker-entrypoint.sh"]
 
 CMD ["help"]