Backport of servicedisco: ensure service uniqueness in job validation into release/1.2.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #13869 to be assessed for backporting due to the inclusion of the label backport/1.2.x.

WARNING automatic cherry-pick of commits failed. Commits will require human attention.

The below text is copied from the body of the original PR.

---

87ef517: some cleanup to use set in the validateServices function

0cc1833: track uniqueness of services in validateServices function

Fixes #13814

Closes #13836 - This PR went in the other direction - to support groups with services that had the same <name, task|group, port_label>. The change is gnarly - basically we would need to add something like a hash of the tags of a service to the unique ID generated by MakeAllocationServiceID - which is then used as an index in the state store. All services with tags would be given new IDs, causing unwanted churn in large clusters. The benefit doesn't come close to justifying the means, so I'm going to abandon the feature and just validate the intrinsic invariant we already have (see: this PR).

Spot check:

example validation on identical services with port label set

Error submitting job: Unexpected response code: 500 (1 error occurred:
	* Task group database validation failed: 1 error occurred:
	* Task group service validation failed: 1 error occurred:
	* Services are not unique: [group->db:p1]

same but without port label set

Error submitting job: Unexpected response code: 500 (1 error occurred:
	* Task group database validation failed: 1 error occurred:
	* Task group service validation failed: 1 error occurred:
	* Services are not unique: [group->db]

job file

job "simple" {
  datacenters = ["dc1"]
  type        = "service"

  group "database" {

    service {
      name     = "db"
      tags     = ["two"]
      # port = "p1"
      provider = "nomad"
    }

    service {
      name     = "db"
      tags     = ["one"]
      # port = "p1"
      provider = "nomad"
    }

    task "db" {
      driver = "raw_exec"
      config {
        command = "bash"
        args    = ["-c", "sleep 15000"]
      }
    }
  }
}

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[shoenig]

This is largely NSD code ... which doesn't exist in 1.2.x

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