SCORU/Node: allow to run without a configuration file

Context

Fixes #4212 (closed).

This MR allows for the rollup node to be run without a configuration file. If one is provided, the arguments on the command line take precedence over the values set in the configuration file.

An additional run command is provided which allows to override some operators:

run <mode> for <smart-rollup-address> with operators [<operator>...]

Manually testing the MR

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