Feat/auto emails

[janekhuong]

Tickets:

• HAC-

List of changes:

• Added backend functionality for sending batch decision emails

Type of change

• New feature (non-breaking change which adds functionality)

How has this been tested?

Create test hackers with valid email addresses. In staff dashboard, change their statuses to accepted/declined. Click "Send Emails" button, choose to send acceptance or declined emails, and then confirm.

Questions for code reviewers?

• Middleware.Auth.ensureAuthorized() calls in emails.js is failing; commented out for now but will figure it out

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• Listed change(s) in the Changelog
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published in downstream modules