graph: Enable the shm mount on Maxxi

I never learned Puppet and this is completely untested, so please review carefully

This enables the /dev/shm mount of swh-graph on Maxxi, so I can run queries on the graph efficiently there, instead of mmaping from disk

And for this to work, you need to:

1. Rename/replace /srv/softwareheritage/ssd/datasets/2023-09-03 to /srv/softwareheritage/ssd/datasets/2023-09-06 (it's a mountpoint that contains no data, looks like someone made a typo)
2. move data from /srv/softwareheritage/ssd/data/vlorentz/datasets/2023-09-06/compressed/ to /srv/softwareheritage/ssd/datasets/2023-09-06/compressed/
3. symlink /srv/softwareheritage/ssd/datasets/latest to /srv/softwareheritage/ssd/datasets/2023-09-06/