Spike: Evaluate moving directly to a FixedItemsModel

Problem

The plans table migration to a static table will take several milestones for a safe migration. It may be possible to speed the transition by moving directly to a FixedItemsModel.

• Evaluate the complexity of moving directly to a FixedItemsModel
• Identify risks and dependencies
• Create a basic POC to validate the transition

Proposal

1. Create a new static FixedItemsModel.
2. Migrate table references and application code to simultaneously reference the new model and existing model.
3. Backfill the references to the new table with a migration.
4. Drop the old table and model.

Similar to this MR.

This way we could enable using the new table with a feature flag to confirm functionality.

Concerns

• This could cause extra work to maintain parity between the two models functionality beyond just the database tables.