dynamic host volumes: policy-override flag on CLI

[tgross]

The create/register volume RPCs support a policy override flag for soft-mandatory Sentinel policies, but the CLI and Go API were missing support for it.

Also add support for Sentinel warnings to the Go API and CLI.

Ref: #24479

---

Testing with the following policy file:

has_tag = func() {
  print("volume is missing tag")
  tag = volume.parameters["tag"] else 0
  return tag is not 0
}

main = rule { has_tag() }

After applying this branch on top of https://github.com/hashicorp/nomad-enterprise/pull/2087:

$ nomad sentinel apply -scope=submit-volume -level=soft-mandatory no-untagged-volumes ./policy.hcl
Successfully wrote "no-untagged-volumes" Sentinel policy!

$ nomad volume create ./demo/hostvolume/host.volume.hcl
Error creating volume: Unexpected response code: 500 (1 error occurred:
        * no-untagged-volumes : Result: false

Print messages:

volume is missing tag

no-untagged-volumes:7:1 - Rule "main"
  Value:
    false)

$ nomad volume create -policy-override ./demo/hostvolume/host.volume.hcl
==> Created host volume test with ID 533bd0e0-ec17-2607-97b4-56eb2079aaad
  ⠦ Monitoring volume "533bd0e0" in progress...

    2024-12-02T16:07:59-05:00
    ID        = 533bd0e0-ec17-2607-97b4-56eb2079aaad
    Name      = test
    Namespace = default
    Plugin ID = example-host-volume
    Node ID   = 876ae9a8-4a89-1f50-2d87-a8ecdd01be5b
    Node Pool = default
    Capacity  = 47 MiB
    State     = pending
    Host Path = /run/nomad/dev/alloc_mounts/533bd0e0-ec17-2607-97b4-56eb2079aaad^C

[pkazmierczak]

👍