fix(healthcare): replace deprecated NotificationConfig with FhirNotificationConfig

[noerog]

Description

Fixes b/310269530

Checklist

• [X] I have followed Contributing Guidelines from CONTRIBUTING.MD
• [X] Tests pass: go test -v ./.. (see Testing)
• [X] Code formatted: gofmt (see Formatting)
• [X] Vetting pass: go vet (see Formatting)
• [X] Please merge this PR for me once it is approved

[snippet-bot[bot]]

No region tags are edited in this PR.

This comment is generated by snippet-bot. If you find problems with this result, please file an issue at: https://github.com/googleapis/repo-automation-bots/issues. To update this comment, add snippet-bot:force-run label or use the checkbox below:

• [ ] Refresh this comment