Setup fluxcd's log dir and logrotate

- Armada has been replaced by Fluxcd, so the logrotate config can
be adapted.

- An entry was added to /etc/tmpfiles.d to create /var/log/flux
during boot. Some more context in [1].

- About the owner:group:
The flux container processes are associated with the user:group
'nobody:nogroup' as defined in their Dockerfiles [2,3], which is
a default user with very restricted privileges [4].
Since /var/log is owned by root, it does not allow flux to write files.
To circumvent that, /var/log/flux has its ownership set to match
the container processes.

[1] https://review.opendev.org/c/starlingx/config-files/+/859666
[2] https://github.com/fluxcd/source-controller/blob/v0.32.1/Dockerfile#L87
[3] https://github.com/fluxcd/helm-controller/blob/v0.27.0/Dockerfile#L44
[4] https://wiki.debian.org/SystemGroups

Test Plan:
PASS build custom iso and install. Flux log dir exists
     and has right owner:group.
PASS logs rotate

Partial-Bug: 2009784

Signed-off-by: Leonardo Fagundes Luz Serrano <Leonardo.FagundesLuzSerrano@windriver.com>
Change-Id: I8bf8bf5f42c78d6ddab8f0d65e6ffaff9a8ec555

syslog-ng-config/debian-source/syslog-ng.logrotate

@@ -75,7 +75,7 @@
 /var/log/collect.log
 /var/log/ldapscripts.log
 /var/log/tuned/tuned.log
-/var/log/armada/*.log
+/var/log/flux/*.log
 {
         nodateext
         size 10M

systemd-config/source-debian/stx-tmpfiles.conf

@@ -30,3 +30,6 @@ d /var/log/puppet 0755 puppet puppet -
 
 # watchdog
 d /var/log/watchdog 0750 root root -
+
+# fluxcd
+d /var/log/flux 0755 nobody nogroup -