What

This MR adds the following GET RPCs:

/health: Returns an empty response if the rollup node can answer requests
/version: Returns the version information of the rollup node
/stats/ocaml_gc: Gets stats from the OCaml Garbage Collector
/stats/memory: Gets memory usage stats
/config: Returns the full configuration of the running rollup node

Why

These can be useful for end users and rollup operators (health, version, ...) as well as to troubleshoot the rollup node.