[subsystem-benchmarks] Save results to json (#3829)

Here we add the ability to save subsystem benchmark results in JSON
format to display them as graphs

To draw graphs, CI team will use
[github-action-benchmark](https://github.com/benchmark-action/github-action-benchmark).
Since we are using custom benchmarks, we need to prepare [a specific
data
type](https://github.com/benchmark-action/github-action-benchmark?tab=readme-ov-file#examples):
```
[
    {
        "name": "CPU Load",
        "unit": "Percent",
        "value": 50
    }
]
```

Then we'll get graphs like this: 

![example](https://raw.githubusercontent.com/rhysd/ss/master/github-action-benchmark/main.png)

[A live page with
graphs](https://benchmark-action.github.io/github-action-benchmark/dev/bench/)

---------

Co-authored-by: ordian <write@reusable.software>

polkadot/node/network/availability-recovery/benches/availability-recovery-regression-bench.rs

@@ -28,6 +28,7 @@ use polkadot_subsystem_bench::{
 	},
 	configuration::TestConfiguration,
 	usage::BenchmarkUsage,
+	utils::save_to_file,
 };
 use std::io::Write;
 
@@ -58,7 +59,13 @@ fn main() -> Result<(), String> {
 		})
 		.collect();
 	println!("\rDone!{}", " ".repeat(BENCH_COUNT));
+
 	let average_usage = BenchmarkUsage::average(&usages);
+	save_to_file(
+		"charts/availability-recovery-regression-bench.json",
+		average_usage.to_chart_json().map_err(|e| e.to_string())?,
+	)
+	.map_err(|e| e.to_string())?;
 	println!("{}", average_usage);
 
 	// We expect no variance for received and sent