* Alerting: Add action, scope, role_id to permission table
The existing role_id, action, scope index has the wrong ordering to be most
effectively used in dashboard/folder permission requests.
On a large tests set, the slow database calls were on the order of ~30-40ms, so
when performed individually they don't have that large of a latency impact.
However, when done in bulk in the migration this adds up to some very slow
requests.
After the index is added these same database calls are reduced to ~4-5ms
* Change index to action, scope, role_id
* Make new index unique and drop [role_id, action, scope] index
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