Add two or more races column to application export

[bencodeorg]

Adds a column to the teacher application gsheet export that the outreach team had been manually generating, saying whether a teacher identified as part of two or more racial groups.

Testing story

I tested this new code worked on a single application selected in the rails console.

Reviewer Checklist:

• Tests provide adequate coverage
• Privacy and Security impacts have been assessed
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked