Backport of [ui] Read-based checks for viewing templates and write-based checks for saving them into release/1.8.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #23458 to be assessed for backporting due to the inclusion of the label backport/1.8.x.

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

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This adds nuance to the ACL policy checks for a user to be able to see Job Templates (which are specifically-named Nomad Variables behind the scenes).

The way it works today has some specific checks in place:

• to even get into the job templates section, you have to first click the "Run Job" button, which only exists if you have the submit-job ACL capability, or a general "write" policy.
• Once there, we only show you a "Choose from template" button if you can write variables to *.

I think the original intent here was to do up-front checks for full CRUD access, but this PR moves that access check a little downstream. Here, you'll see that the check to see the "Choose from template" button requires specifically read variable access (and I could be convinced to make it list variables, but that would make the subsequent page pretty useless), and the write variable check is moved downstream to the "save as template" button, and to manually edit a given job template via the Management page.

Here is a sample ACL policy to test with:

namespace "default" {
  policy = "read"
  capabilities = ["submit-job"]
  variables {
    # give read access to all job templates related to this namespace
    path "nomad/job-templates/*" {
      capabilities = ["read","list","write"]
    }
    path "*" {
      capabilities = ["write","list"]
    }
  }
}

^--- the submit-job capability is in place, so the "Run Job" button will be present. Also, the nomad/job-templates/* rule has both read and write, which will show both a "Choose from template" and a "Save as template" button. Remove either read or write to see how buttons disappear accordingly.

User has read and write, but not delete, variable capability:

User has read variables for nomad/job-templates/*:

User has write variables for nomad/job-templates/*:

Resolves #23438

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Overview of commits

• bbd1bb3

[github-actions]

Ember Test Audit comparison

	release/1.8.x	2c61a7e	change
passes	1564	1564	0
failures	2	2	0
flaky	0	0	0
duration	000ms	000ms	-000ms