helm chart: Ensure aptly can write to /tmp without root

After changing the aptly service user from admin to a non-privileged account, additional directories were configured to grant the necessary write permissions. However, the /tmp folder, required for temporary files, was omitted. While other projects address this by adding /tmp as an extraVolume, we must explicitly include it in the Helm chart due to its critical role rather than leaving it as an optional configuration.

Signed-off-by: Pablo Vigo pvigo@collabora.com