Add helm chart for central deployment

[tpoliaw]

This is partially covered by #22 and #23 but is retrospectively adding requirements before they are merged.

Helm chart needs to

• Set environment variables for
  • DB location
  • Port
  • Tracing host/level
  • Auth host/queries
  • GDA tracker root directory
• Create a PVC for the DB storage
• Mount the DB directory somewhere useful
• Mount the directories required to interoperate with GDA installations
• Run the process as a user that has write access to GDA var directories
• Backup the DB/configuration to some out of k8s storage so it can be restored easily
  • Restore from backup if available when first deployed - may require code changes?

[tpoliaw]

The PVC is created with a retention policy of keep so the PV 'should' be reused between deployments. The backup of the PV is left to the infrastructure team but from scicomp:

The "netapp" volumes are backed up by the NetApp system with these rules:

• Daily incremental backups
• Monthly full backups
• Backups are retained for 6 months

This should be enough for our purposes, especially when the file numbers are being synced to/from the var directories as well.

The GDA var directories should be mounted as required via the 'extraVolumes' and 'extraVolumeMounts' configuration in values.yaml.