### What changes were proposed in this pull request?
This PR adds an JDK11-based build example in `bin/docker-image-tool.sh`.
### Why are the changes needed?
This helps the users migrate to JDK11 more easily.
### Does this PR introduce any user-facing change?
Yes, but this is a usage help.
### How was this patch tested?
First, check the help usage manually.
```
$ bin/docker-image-tool.sh -h
...
- Build and push JDK11-based image with tag "v3.0.0" to docker.io/myrepo
bin/docker-image-tool.sh -r docker.io/myrepo -t v3.0.0 -b java_image_tag=11-jre-slim build
bin/docker-image-tool.sh -r docker.io/myrepo -t v3.0.0 push {code}
```
Then, build the image and check Java version.
```
$ docker run -it --rm docker.io/myrepo/spark:v3.0.0 java --version | tail -n3
openjdk 11.0.6 2020-01-14
OpenJDK Runtime Environment 18.9 (build 11.0.6+10)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.6+10, mixed mode)
```
Closes#28171 from dongjoon-hyun/SPARK-31401.
Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
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