L2/Node: Separate Etherlink and Tezlink aspects in the node

What

Try separate Etherlink and Tezlink aspect in the storage

Why

Currently, the durable storage module is a module containing every function related to the durable_storage, access etherlink values, tezlink values, rollup values.

This MR tries to separate everything by introducing Etherlink_durable_storage and Tezlink_durable_storage.

There's also the service_backend_sig that include every Etherlink function at top level and having a Tezlink backend module, the MR introduce a standard of having Etherlink_backend and Tezlink_backend. This makes a lot of codes move in the first commits.

The goal of this refacto is to make it easier for everyone to know when we're in a specific Etherlink context or Tezlink context. The idea emerged from this MR !17771 (merged) that parametrize Blocks access depending on the root of the chain Tezlink or Etherlink. In the node, some path were hard coded as an Etherlink path but it was hard to know why when the code is in durable_storage.ml. In comparison now, if the path is hardcoded with Etherlink path in a etherlink_durable_storage.ml file, it's easier.

How

Manually testing the MR

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