Update terraform configuration for demo/csi/digitalocean

[DerekStrickland]

This PR updates the demo/csi/digitalocean terraform files in the following ways

• Updates main.tf to use the new capability stanza
• Updates volume-job.nomad to include required access_mode and attachment_mode properties in the volume stanza
• Adds the recently introduced terraform.lock.hcl file

[lgfa29]

Thanks! I just pushed a commit to format some of the HCL files.

[github-actions]

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