Add Datadog monitor to ITF VA Notify confirmation

[ataker]

Summary

Add datadog monitors to ITF's Va Notify events

Related issue(s)

Datadog: Monitor VA Notify Callbacks and Surface Failures for ITF email #132142

Testing done

• New code is covered by unit tests

Screenshots

Note: Optional

What areas of the site does it impact?

n/a

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Events are being sent to the appropriate logging solution
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Feature/bug has a monitor built into Datadog (if applicable)
• If app impacted requires authentication, did you login to a local build and verify all authenticated routes work as expected
• I added a screenshot of the developed feature

Requested Feedback

(OPTIONAL)What should the reviewers know in addition to the above. Is there anything specific you wish the reviewer to assist with. Do you have any concerns with this PR, why?