Add --header to benchmark overhead + storage (#12204)

* Add header to 'overhead' command

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Add header to 'storage' command

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Update READMEs

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <info@kchr.de>

* .as_ref() and fmt

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Bastian Köcher <info@kchr.de>

substrate/utils/frame/benchmarking-cli/src/overhead/template.rs

@@ -51,6 +51,8 @@ pub(crate) struct TemplateData {
 	hostname: String,
 	/// CPU name of the machine that executed the benchmarks.
 	cpuname: String,
+	/// Header for the generated file.
+	header: String,
 	/// Command line arguments that were passed to the CLI.
 	args: Vec<String>,
 	/// Params of the executed command.
@@ -70,6 +72,12 @@ impl TemplateData {
 		stats: &Stats,
 	) -> Result<Self> {
 		let weight = params.weight.calc_weight(stats)?;
+		let header = params
+			.header
+			.as_ref()
+			.map(|p| std::fs::read_to_string(p))
+			.transpose()?
+			.unwrap_or_default();
 
 		Ok(TemplateData {
 			short_name: t.short_name().into(),
@@ -79,6 +87,7 @@ impl TemplateData {
 			date: chrono::Utc::now().format("%Y-%m-%d (Y/M/D)").to_string(),
 			hostname: params.hostinfo.hostname(),
 			cpuname: params.hostinfo.cpuname(),
+			header,
 			args: env::args().collect::<Vec<String>>(),
 			params: params.clone(),
 			stats: stats.clone(),