BAU: Adjust auth journey completion rate alarm

[cearl1]

Wider context of change

The auth journey rate alarm has been going off a bit too much recently. We should adjust it so its not as sensitive.

What’s changed

This PR reduces the journey completion rate % threshold from 50% to 30%, and increases the minimum amount of traffic from 160 to 250.

Checklist

• Lambdas have correct permissions for the resources they're accessing.
• Impact on orch and auth mutual dependencies has been checked.
• Changes have been made to contract tests or not required.
• Changes have been made to the simulator or not required.
• Changes have been made to stubs or not required.
• Successfully deployed to authdev or not required.
• Successfully run Authentication acceptance tests against sandpit or not required.
• Added new endpoints to local running (LocalOrchestrationApi.java) or not required.

[github-actions]

Java Tests Skipped

No Java files were changed in this pull request. Java tests will be skipped¹.

Any Java files that are changed in a subsequent commit will trigger the Java tests.

Footnotes

1. These tests will still show as passing in the PR status check, but will not actually have run. ↩

[Louisasa]

we should update the message to be 30%