[CPDNPQ-2411] Redact to addresses in mailer logs

[rwrrll]

Context

Ticket: https://dfedigital.atlassian.net/browse/CPDNPQ-2411

When Rails mailers process and deliver outbound mail, recipient addresses are leaking into Rails log output, which is a PII concern.

• We can't use Rails filter_parameters because it doesn't cover mailer parameters, only HTTP requests.
• Rails Semantic Logger has filtering functionality, but it's primarily for dropping entire lines, implementing redaction felt too complex/heavy.
• So the solution I've gone with is to intercept and redact the incoming event as it flows through the log stack by prepending a simple module.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Review app deployed to https://npq-registration-review-2216-web.test.teacherservices.cloud/