XNAT volume configuration, implement better control of structure

[dean-taylor]

Allow a more complex configuration of XNAT volumes. This includes more control over the paths of standard volume locations as well as the matching or amalgamation of paths to volumes in different combinations.

Previously the volumes matched the default paths. This was due to the helm chart not being able to alter the pre-setup values and an initial deployment of potentially mismatched paths to volumes as a manual step. Code and configuration have been added to XNAT and the Helm chart to make this available.

STEPS.
Formulate a best practice as default options within the Helm charts values file.
Add the template changes to allow the values to be presented to the initial setup step to ensure consistency.