Specification for a two-way Ethereum bridge

[gordsport]

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

[davidsiska-vega]

Closing as duplicated by #1132