Proto/RPC: move all RPCs to Plugin

Owner of the MR: @rafoo_.

Stacked on !17517 (merged) to avoid losing RPC documentation.

Also blocked on !17512 (merged) to avoid conflicts.

What

This MR moves all protocol RPCs to the plugin.

Why

• Make these RPCs more maintainable: updating the plugin requires an Octez release which is much lighter to propose than a protocol update. That's why the RPC plugin was introduced in the first place.
• Simplify the model: we won't have to remember which RPC is defined in the protocol and which is defined in the plugin because everything will be in the plugin.
• Unlock further simplifications: if the protocol does not need to handle RPCs, we can remove large pieces from the environment (all of Resto and we don't need to expose shell errors anymore).

How

• move the *_services.ml{,i} files and update the path.

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