Lib_protocol_environment: Adding a duo context option

What

This MR allows to use Brassaia and Irmin in parallel

Why

This will allow anyone working on Brassaia to check if the changes are coherent with Irmin's behaviour.

How

By creating a new option for TEZOS_CONTEXT_BACKEND, Duo, and by adding a wrapper that shares the same signature with irmin and brassaia and execute the functions coming from both, compare their results and returns the result if they're equal.

Manually testing the MR

TEZOS_CONTEXT_BACKEND=Duo ./octez-run or any other octez executable

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR