[CST] - Add feature flag cst_send_evidence_submission_failure_emails

[pmclaren19]

Summary

• Created a feature flag cst_send_evidence_submission_failure_emails

Related issue(s)

• *Link to ticket created in va.gov-team repo [CST] Merge feature branch for silent failure work into master va.gov-team#100037

Testing done

• Ran locally and I see feature flag

Screenshots

Images of new feature flag

What areas of the site does it impact?

CST

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