Rename jenkins-slave to jenkins-agent
The term of slave
has been deprecated since 2016 by Jenkins upstream,
they then replaced master
by controller
which we have adjusted to
already.
This is the part of the switch to rename the jenkins-slave
unix user
to jenkins-agent
. It requires some Puppet change which holds the
detailled instruction to do the migration:
https://gerrit.wikimedia.org/r/c/operations/puppet/+/922555
Bug: T254646