Use the latest supported tags when not specifying any tag for servlet containers and databases

Right now, the config is located in https://github.com/xwiki/xwiki-jenkins-pipeline/blob/05000b1450ceba1dd05f7b7821895502adc6b692/vars/dockerConfigurations.groovy#L37-L50

The idea is to move that info into XWiki platform's top level pom.xml using a syntax like:

xwiki.docker.<server id>.latest=<tag>
xwiki.docker.<server id>.lts=<tag>

e.g.

xwiki.docker.mysql.latest=8

Then we'll need to:

• Refactor ServletContainerExecutor and DatabaseContainerExecutor to read the latest versions from the pom when no tag is specified
• Refactor https://github.com/xwiki/xwiki-jenkins-pipeline/blob/05000b1450ceba1dd05f7b7821895502adc6b692/vars/dockerConfigurations.groovy#L37-L50 to read from the pom.xml. The solution is to use calls like:

  def version = sh script: 'mvn help:evaluate -Dexpression=xwiki.docker.mysql.latest -q -DforceStdout', returnStdout: true

• Refactor https://www.xwiki.org/xwiki/bin/view/Macros/ProductVersionMacro/ to read from the master platform pom.xml to extract the versions instead of reading from the groovy pipeline file + ideally also read from the pom.xml of the xwiki LTS branch.

Pros:

• Simpler for devs which don't have to be careful to always specify a tag (although it's good to know with what version you're testing )
• The supported versions can depend on the branch