add dispatch idempotency token support in the CLI

[lgfa29]

Sample outputs:

$ nomad run dispatch.nomad
Job registration successful

$ nomad job dispatch --idempotency-token=1 dispatch
Dispatched Job ID = dispatch/dispatch-1634856177-4c79b169
Evaluation ID     = e70ffa47

==> 2021-10-21T18:42:57-04:00: Monitoring evaluation "e70ffa47"
    2021-10-21T18:42:57-04:00: Evaluation triggered by job "dispatch/dispatch-1634856177-4c79b169"
    2021-10-21T18:42:57-04:00: Allocation "704c7b95" created: node "d895588c", group "batch"
==> 2021-10-21T18:42:58-04:00: Monitoring evaluation "e70ffa47"
    2021-10-21T18:42:58-04:00: Evaluation status changed: "pending" -> "complete"
==> 2021-10-21T18:42:58-04:00: Evaluation "e70ffa47" finished with status "complete"

$ nomad job dispatch --idempotency-token=1 dispatch
Dispatched Job ID = dispatch/dispatch-1634856177-4c79b169

$ nomad job status dispatch/dispatch-1634856177-4c79b169
ID                = dispatch/dispatch-1634856177-4c79b169
Name              = dispatch/dispatch-1634856177-4c79b169
Submit Date       = 2021-10-21T18:42:57-04:00
Type              = batch
Priority          = 50
Datacenters       = dc1
Namespace         = default
Status            = running
Periodic          = false
Parameterized     = false
Idempotency Token = 1

Summary
Task Group  Queued  Starting  Running  Failed  Complete  Lost
batch       0       1         0        0       0         0

Allocations
ID        Node ID   Task Group  Version  Desired  Status   Created  Modified
704c7b95  d895588c  batch       0        run      pending  10s ago  6s ago

Closes #10641

[DerekStrickland]

I have no current request for change, but I am following @notnoop 's discussion.

[github-actions]

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