Maven installation in Slave should make use of Nexus as proxy

[deors]

Maven installation in Slave should make use of Nexus as proxy, optimizing bandwidth when downloading artefacts from public repositories, and enabling deployment of artefacts built in ADOP builds.

Executing this command:
$ sudo docker exec jenkins-slave cat tools/hudson.tasks.Maven_MavenInstallation/ADOP_Maven/conf/settings.xml
I can see that Maven configuration is the vanilla one.

We should evaluate which mechanism would be the better to have Maven settings appropriately loaded into the Slave:
a) Do this during Platform init
b) Install Maven along with our settings in Dockerfile (vs. automatic install)
c) Any other.