Use reproducible builds by default

[jonenst]

Signed-off-by: HARPER Jon jon.harper87@gmail.com

Please check if the PR fulfills these requirements (please use '[x]' to check the checkboxes, or submit the PR and then click the checkboxes)

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem ? If so, link to this issue using '#XXX' and skip the rest
NO

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
bugfix

What is the current behavior? (You can also link to an open issue here)
by default builds are not byte for byte reproducible (jar, docker images, itools packager zip)

What is the new behavior (if this is a feature change)?
by default builds are byte for byte reproducible (jar, docker images, itools packager zip)

Does this PR introduce a breaking change or deprecate an API? If yes, check the following:
NO

Other information:
needs a fix for itools packager, and a change in the code that puts the real current time in a java-template in powsybl-core/tool or other projecst ( @autoservice(Version.class) system)

[olperr1]

Note that starting with release 2.9.0 of versions-maven-plugin, versions:set goal updates the project.build.outputTimestamp property (source).
#38 will upgrade the plugin to a version supporting this mechanism.