Jaeger spans for availability distribution (#2559)

* Logging functionality for spans.

* Jaeger spans for availability distribution.

* Fix instrumentation to use log target properly.

* Add some tracing instrumentation macros.

* Use int_tags instead of logs.

* Add span per iteration.

* Remove span::log functionality.

* Fix instrumentation log target for real.

* Add jaeger span to responding side as well.

* Revert "Fix instrumentation log target for real."

This reverts commit e1c2a2e6ff6f257e702f07d8a77c2668af92b0ef.

* Revert "Fix instrumentation to use log target properly."

This reverts commit 7caa0bd1acc6fe9727bb3a91851560d756c40ab8.

* target -> subsystem in instrumentatio macro

target is not correct either, and the correct way of using a top level
target = LOG_TARGET does not work, as the macro expects a string literal
and gets confused by the constant `LOG_TARGET`.

* Use kebab-case for spa names.

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

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

polkadot/node/network/availability-distribution/src/requester/mod.rs

@@ -74,6 +74,7 @@ impl Requester {
 	///
 	/// You must feed it with `ActiveLeavesUpdate` via `update_fetching_heads` and make it progress
 	/// by advancing the stream.
+	#[tracing::instrument(level = "trace", skip(keystore, metrics), fields(subsystem = LOG_TARGET))]
 	pub fn new(keystore: SyncCryptoStorePtr, metrics: Metrics) -> Self {
 		// All we do is forwarding messages, no need to make this big.
 		// Each sender will get one slot, see
@@ -90,6 +91,7 @@ impl Requester {
 	/// Update heads that need availability distribution.
 	///
 	/// For all active heads we will be fetching our chunks for availabilty distribution.
+	#[tracing::instrument(level = "trace", skip(self, ctx, update), fields(subsystem = LOG_TARGET))]
 	pub async fn update_fetching_heads<Context>(
 		&mut self,
 		ctx: &mut Context,