feat: add healthcheck logs for Notify callback

[patheard]

Summary

Add healthcheck logging for Notify callback behaviour. This will allow us to monitor callback behaviour on the service health dashboard.

Test instructions | Instructions pour tester la modification

1. Happy path: submit a form with a valid email address and expect to see the log that no reprocessing is required.
2. Unhappy path: submit a form with an invalid email address and expect to see the permanent failure log message.

Unresolved questions / Out of scope | Questions non résolues ou hors sujet

None

Pull Request Checklist

Please complete the following items in the checklist before you request a review:

• [x] Have you completely tested the functionality of change introduced in this PR? Is the PR solving the problem it's meant to solve within the scope of the related issue?
• [x] The PR does not introduce any new issues such as failed tests, console warnings or new bugs.
• [x] If this PR adds a package have you ensured its licensed correctly and does not add additional security issues?
• [x] Is the code clean, readable and maintainable? Is it easy to understand and comprehend.
• [x] Does your code have adequate comprehensible comments? Do new functions have docstrings?
• [ ] Have you modified the change log and updated any relevant documentation?
• [x] Is there adequate test coverage? Both unit tests and end-to-end tests where applicable?
• [ ] If your PR is touching any UI is it accessible? Have you tested it with a screen reader? Have you tested it with automated testing tools such as axe?

[github-actions[bot]]

:test_tube: Review environment

https://oky3xscujtwvhrecqiyiorpzge0mpqzi.lambda-url.ca-central-1.on.aws/

[patheard]

Test results from the PR review env: