[SPEC ONLY] Two way ethereum bridge for hybrid/passive liquidity

[gordsport]

Two way bridge (lite) would basically be:

• allow committing funds to passive liquidity and fund accounts via an Ethereum transaction
• allow removing funds from passive liquidity and fund accounts via an Ethereum transaction
• allow getting data about passive liquidity pools and fund accounts via an Ethereum transaction
• ideally do the above in a way that would make it possible to use them with liquidity aggregator and smart routing protocols

Note we obviously can't spec all of this now or fully implement it because we don't have the core features it would be used with, but hopefully we can start thinking about how we'd do this and spec the mechanisms for the Ethereum contract to use and for interaction between the chains now.

The reason for these is they gas prices are prohibitive for trading on a two way bridge really but a longer term parking of funds for yield may make more sense.

[davidsiska-vega]

This was on a duplicate issue so I am copying here and will close #878 ,

In order to be ready for Q2 2022 development we need to agree upon the scope for the engineering team to deliver in this time period.

We need a specification for a two-way Ethereum bridge. Further details related to the prioritisation meeting can be seen on the Notion Board

Can this be an extension to 0031-ETHB-ethereum_bridge_spec.md or should it be a new spec. I think @C0deMunk33 suggested this would be a new smart contract and not an update to the existing bridge.

How do we know when we are done:

The spec has been updated to indicate what are the requirements for flexible oracles and basic combinators
The specification contains acceptance criteria with IDs that reflect the scope of the work required for Q2 2022
The engineering team has reviewed the specifications and understand the scope
The spec is merged into the specs repo before engineering start development/test work

[gordsport]

Blocked:
Should be done once we have a good understanding of:

• [SPEC ONLY]: Gather requirements for fund accounts #866