rpc_api.md: account for previous RPC API updates

Address description changes from:

* proc_apply_schema_change — picodata@d6ef15ca (`24.5.0-310`)
* proc_runtime_info:
    * add `slab_info` — picodata@eafa4991 (`24.6.0-17`)
    * add `governor_step_counter` — picodata@641e8383 (`24.7.0-12`)
* proc_sharding_bootstrap — picodata@d2a5c35e (`24.6.0-74`)