Allow multiple vault types for a given collateral type

What is the Problem Being Solved?

The vaults system manages its risk and business-level competitiveness through governed parameters such as the liquidation threshold, stability fees, and minting limit.

Currently, for a given collateral type, it is only possible to have a single vault type (i.e., one set of governed parameters for all vaults of a given collateral).

To allow a more diverse set of options for users, it will be beneficial to have multiple vault options for a given collateral type. For example, MakerDAO currently employs this by offering vaults that accept ETH at different minimum collateralizations and interest rates, eg:

ETH-A vaults at 165% MCR, 140% Liquidation Ratio and 1.5% interest
ETH-B vaults at 130% MCR, 110% Liquidation Ratio and 7.0% interest
ETH-C vaults at 200% MCR , 165% Liquidation Ratio and 0.5% interest

This allows the system to incentivize greater overcollateralization by charging less for it.

Description of the Design

each vault manager goes into agoricNames
probably agoricNames.objects since that’s how they’ll be used. that they’re vault managers isn’t important for the lookup table.
enumeration of vault managers (for use to pick among them) will be through data in vstorage
a new InvitationSpec for source: object will allow a smart wallet transaction to call makeVaultInvitation on the manager object https://github.com/Agoric/agoric-sdk/issues/6850

Security Considerations

Acceptance Criteria

New vault type for an already-accepted collateral can be added by the Economic Committee (note: was previously scoped as a BLDer DAO vote but EC input was strongly in favor of it being under their control)
Vault types have isolated governed parameters which can be adjusted through an EC vote
User may have multiple vault types of a given collateral open simultaneously
Retail vault options visible and interactive for all app users
Institutional vault options only visible and interactive to pre-approved/white-listed addresses (addresses that are white-listed by the EC)

Agoric / agoric-sdk