v2.1.0-preview.4.2

Highlights:
This sprint focused on some behind-the-scenes validation refactoring and maintenance work, some network performance improvements, and a small number of defect fixes.

Specific improvements:

• [USER] Require applicant to supply at least 1 email under Information about you —> Your contact information [EN-3651]
• Clear out state field when toggling Citizenship Status —> Place of issuance from In the U.S. to Outside the U.S. [EN-3433]
• Remove DSN option until we determine a mechanism to round-trip the phone numbers from IM/e-QIP [EN-3667]
• Minor text copy changes for 85 and 86 [EN-3653]

New configuration variables:
Add HTTP header to direct the browser to cache CORS preflight responses (CORS_MAX_AGE) [EN-31433]
Add ability to set PostgreSQL sslmode (DATABASE_SSLMODE)