Configure the size of /dev/shm in skaha user sessions

[pharaofranz]

Some packages such as DDFacet make use of the shared memory at /dev/shm (check this link). It would be nice if /dev/shm has the same size as the RAM requested by the user; or at least something larger than the default 64 MB.

[brianmajor]

Adding a comment on how this can be accomplished by forking the canfar charts, but this issue is for a more general, configurable solution.

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Give the directory space on the node through a mounted k8s emptyDir that maps to (overwrites) /dev/shm.  This is done by modifying the appropriate launch script, here:
    https://github.com/opencadc/deployments/blob/main/helm/applications/skaha/skaha-config

With these changes:

Add a volume:

- name: dshm-volume
      emptyDir:
        medium: Memory
        sizeLimit: "1Gi"

Mount it to the session :

- volumeMounts:
  - mountPath: /dev/shm
    name: dshm-volume