Add comments to Dockerfile to trigger Docker Image creation with JDK 17 and Redis 6.2.

This is necesarry in order to produce Spring Data Redis 3.0.0-SNAPSHOTs.

Thus far, the Jenkins CI build for 3.0.x is failing due to (from build #1):

"19:18:16  Stage "Publish JDK 17 + Redis 6.2 Docker image" skipped due to when conditional"

Closes #2173.

ci/openjdk17-redis6.2/Dockerfile

@@ -1,8 +1,10 @@
+# Custom OpenJDK 17 Docker Image
 FROM openjdk:17-bullseye
 
 # Copy Spring Data Redis's Makefile into the container
 COPY ./Makefile /
 
+# Install Redis 6.2
 RUN set -eux; \
 	apt-get update ; \
 	apt-get install -y build-essential ; \