Make some of the contracts upgradable

[ggonzalez94]

This is a bit of a meta issue that requires some discussion before implementing:

• Decide which contracts should be upgradable
• What are the roles required for those contracts
• We have a lot of immutable configurations, especially for contract references. We should decide between the following options:
  • For variables that will never change we are ok leaving them as immutable
  • For variables that we expect to have to change often(e.g. configuration parameters that are sensible to marke changes) they should be storage variables that can be updated by an owner(e.g. a DAO)
  • For variables that we expect to change very infrequently(e.g. a reference to another contract or a config parameter that is not expected to change) I believe the most optimal solution gas wise might be still making it a constant or an internal function that returns a hardcoded value and the way a permissioned actor can update it is by upgrading the contract

[ggonzalez94]

Discussed this during a call yesterday and we have a strong preference towards immutables and internal functions that return a hardcoded value for gas efficiency reasons. Unless absolutely necessary, we should avoid storage variables for config parameters and will instead just upgrade the contract. One downside of this approach is that upgrades will likely have a long delay, while config changes could happen immediately or with shorter delays