[3.9] Docker files for Ehcache

[mathieucarbou]

Backport to 3.9 of #3105

This PR adds a docker folder in the Ehcache kit with instructions on how to build the 3 images, plus the README to place on Docker Hub.

• ehcache-server ehcache-terracotta-server
• terracotta-voter-oss ehcache-terracotta-voter
• terracotta-config-tool-oss ehcache-terracotta-config-tool

Notes:

• I have manually tested them, since it is not yet possible to add docker tests in Ehcache
• Naming still to be discussed
• Gradle / Docker build scripts and deployment to hub.docker.com still to be done in a subsequent PR
• A cherry-pick to the release/3.9 branch can be made once merged

Some ref regarding these required perm / uid:0 with OpenShift (also others): https://docs.openshift.com/container-platform/3.11/creating_images/guidelines.html#openshift-specific-guidelines

TO TEST:

gw assemble
gw distDir
cd clustered/clustered-dist/build/kit/
./docker/buildAndTest.groovy

[mathieucarbou]

Updated READMEs to add the necessary header and footer (licensing, etc) required to be deployed on hub.docker.com

[mathieucarbou]

Added ./docker/buildAndTest.groovy to automate building and testing of images

[mathieucarbou]

Added 3.9-SNAPSHOT tag to built images

[mathieucarbou]

• Changed image names to:

  terracotta/ehcache-terracotta-server
  terracotta/ehcache-terracotta-config-tool
  terracotta/ehcache-terracotta-voter

• Updated ./docker/buildAndTest.groovy to include an Ehcache put/get test

• Fixed base images to azul/zulu-openjdk-alpine:17.0.5-17.38.21

• Added resource filtering in Groovy build script to generate docker files with the correct project version