Automatically approve a change request that is only decreasing quota values

[knikolla]

Depends on nerc-project/coldfront-nerc#132

This is a foundational first step in automating approvals for common PI operations. As this is decreasing a quota, it does not require an admin to confirm the availability of resources requested by the PI.

• Catch signal issued by ColdFront
• Verify that a request is only decreasing values
• Make a decision whether we want to verify that the resource allocation is consuming less resources than the quota decrease requested.
  • If and only if we do
    • implement the functionality in the OpenStack and OpenShift resource allocators to collect current usage data for each quota type
    • verify used <= requested change
• Mark the ChangeRequest as approved and dispatch a change_request_approved signal https://github.com/ubccr/coldfront/blob/0b96bd391136d0a62ee1840e3cae111e6904b999/coldfront/core/allocation/signals.py#L15