[Alerting] Add test to ensure all stack alerts are part of stack alert feature privilege.

[ymao1]

When adding this new stack alert, we forgot to add the alert type id to the stack alerts feature privilege so users with only access to stack alerts would not be able to see this stack alert. We should find a way to ensure this doesn't happen again in the future, maybe with some tests that make sure all available stack alerts are part of the stack alerts feature privilege?

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[mikecote]

Relates (or duplicate?) to #88770. It seems like one option may be to have the test suite (or each test) use the smallest amount of privileges to run successfully.