feat(workflow): Add ProjectTeam model

[macqueen]

Part 1 of 3. This just adds the model + starts filling data. Next steps:

• datamigration to backfill historical data
• actually cut over to use new fields

cc @getsentry/workflow

[ghost]

	1 Warning
⚠️	PR includes migrations

Migration Checklist

• new columns need to be nullable (unless table is new)
• migration with any new index needs to be done concurrently
• data migrations should not be done inside a transaction
• before merging, check to make sure there aren't conflicting migration ids

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