Tezlink/Node: protocols rpc

What

Implement /chains/main/blocks/head/protocols rpc. Return mock values for now.

Prev: tezlink proper setup helpers !17436 (merged)

Why

We need it.

How

Import the corresponding shell rpc.

Manually testing the MR

dune exec etherlink/tezt/tests/main.exe -- tezlink protocols

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