Use / expose resource control capabilities from systemd to ensure Restic stays within safe limits

[frittentheke]

Knowingly Restic can be memory hungry with vastly changing requirements over time. Resticprofile checks for a minimal amount of RAM before Restic is invoked: https://creativeprojects.github.io/resticprofile/usage/memory/index.html

To further ensure Restic does not push the system OOM it might be sensible to also leverage the resource control capabilities of systemd (https://www.freedesktop.org/software/systemd/man/latest/systemd.resource-control.html) like MemoryMax.