Add new tokens_required field for owners table

[trent-codecov]

We need a new default true field for owners (maybe accounts?) to indicate whether tokens are required at all for public repos. tokens_required or similar.

[nora-codecov]

How about upload_token_required_for_public_repos?

Not going to add to Account, I want this to be set per org. Owner table still holds other permission-related fields so I feel like it fits best there. We can add to Account later if need arises.

Wouldn't the default be False?

I'm going to add this as a nullable boolean field with default = False, then backfill all existing orgs to True, then make it non-nullable 👍

[nora-codecov]

I did end up adding this column as default=True because I realized this will act sort of like a feature flag, and should remain True for everyone until we are ready for it to go live.

I'll add a task to this epic to flip the default to False