SCORU/Node: move RPC server outside of protocol and use dynamic directories

Context

This MR moves the RPC server and RPC directories outside of the protocol specific libraries.

Instead of switching the RPC directory (by restarting the server), the protocol specific block directories are now registered as dynamic directories.

Depends on !9105 (merged).

Manually testing the MR

dune exec tezt/tests/main.exe -- -f sc_rollup.ml migration