feat(plugin): add async io for the plugin

[vincenzopalazzo]

Adding the support of the async io for reading to the
std io.

Fixes #98

[vincenzopalazzo]

See

➜  VincentSSD clightning --testnet stop
thread 'main' panicked at /home/vincent/.cargo/git/checkouts/cln4rust-0de0305144cd79e4/1c04dbe/plugin/src/plugin.rs:129:24:
called `Result::unwrap()` on an `Err` value: Os { code: 32, kind: BrokenPipe, message: "Broken pipe" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
{
   "result": "Shutdown complete"
}

[vincenzopalazzo]

not sure we want to use this solution :/