ci: Keep only the artifacts of the last 2 builds (#5383)

Keep only the arfifacts of the last 2 builds

In order to save disk space, the number of builds to keep with artifacts should be limited to 2.

This change should be applied to all branches.

Jenkinsfile

@@ -1,7 +1,7 @@
 node {
     properties([
         disableConcurrentBuilds(abortPrevious: true),
-        buildDiscarder(logRotator(artifactDaysToKeepStr: '', artifactNumToKeepStr: '', daysToKeepStr: '', numToKeepStr: '10')),
+        buildDiscarder(logRotator(artifactDaysToKeepStr: '', artifactNumToKeepStr: '2', daysToKeepStr: '', numToKeepStr: '10')),
         gitLabConnection('gitlab.eclipse.org'),
         [$class: 'RebuildSettings', autoRebuild: false, rebuildDisabled: false],
         [$class: 'JobLocalConfiguration', changeReasonComment: '']