[Scaling] ACL support for new scaling endpoints

[cgbaker]

Definition of done:

• new namespace-scoped ACL capabilities
  • list-scaling-policies
  • read-scaling-policy
  • read-job-scaling
  • scale-job
• create a new coarse-grained, namespace-level policy disposition autoscaler
• the first three should be added to the coarse-grained read policy disposition; all four should be added to write and autoscaler policy dispositions

Child issue of #7394

[cgbaker]

closed by #7418

[github-actions]

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