resolveCiFriendliesOnly should update project.build.outputTimestamp

[ArloL]

To make the adoption of reproducible builds easier it would be great if flatten:flatten with resolveCiFriendliesOnly would also update the build timestamp.

Given

<version>${revision}</version>
<properties>
<project.build.outputTimestamp>2023-01-01T00:00:00Z</project.build.outputTimestamp>
</properties>

When called like this

./mvnw flatten:flatten -Drevision=0.0.9 -Dproject.build.outputTimestamp=2024-01-29T12:23:36+01:00

Would result in

<version>0.0.9</version>
<properties>
<project.build.outputTimestamp>2024-01-29T12:23:36+01:00</project.build.outputTimestamp>
</properties>

That would work for my use case. Maybe a general setting like the one used on the versions-maven-plugin also makes sense.

PS Thanks for the hard work maintaining critical infrastructure like this plugin 🙏🏼