Code Quality Changes

Add

• Specific exceptions for group existing, not existing, or group settings not existing

Fix

• Run Dockerfile as nonroot when needed
• Improve code by using specific exceptions rather than a generic one
• Correct aliases on User records to match the UserAlias record
• Lookup of users by alias, not just email address
• Use constants for repeated error messages
• Use variable instead of hardcoded Staff ID value in tests
• Changed from SHA-1 to SHA-512 like MailAdmin does now
• Remove unnecessary brackets on return values