OAK-10686: parent: add project.build.outputTimestamp property for Reproducable Builds (#1338)

diff --git a/oak-parent/pom.xml b/oak-parent/pom.xml
index 5cb0b82..0816ac4 100644
--- a/oak-parent/pom.xml
+++ b/oak-parent/pom.xml
@@ -34,6 +34,9 @@
   <packaging>pom</packaging>
 
   <properties>
+    <!-- build time stamp: should be updated prior to a release -->
+    <!-- see https://maven.apache.org/guides/mini/guide-reproducible-builds.html -->
+    <project.build.outputTimestamp>1709307307</project.build.outputTimestamp>
     <minimalMavenBuildVersion>3.3.9</minimalMavenBuildVersion><!-- evaluated by ASF parent -->
     <test.opts.memory>-Xmx512m</test.opts.memory>
     <test.opts>${test.opts.coverage} ${test.opts.memory} -XX:+HeapDumpOnOutOfMemoryError -Dupdate.limit=100 -Djava.awt.headless=true</test.opts>