Custom spawn_tasks

[nazar-pc]

Finally we can do this.

Still can't remove sp-session dependency due to RPC layer requiring it (alongside with keystore which consensus chain doesn't have), I'm still thinking what to do about it without copy-pasting a bunch of non-trivial boilerplate.

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[shamil-gadelshin]

Do you mind adding context?

[nazar-pc]

Context is basically in the second commit, PR description and partly in paritytech/polkadot-sdk#5364 mentioned in TODO

We don't need Substrate's prometheus server, we don't want its RPC server in some cases and we also don't want sp-session, though RPC is tightly coupled with it right now unfortunately. Once paritytech/polkadot-sdk#5364 is in our fork we'll no longer need to convert our full configuration data structure into Substrate's Configuration, which will make code simpler and more straightforward.

[shamil-gadelshin]

A small refactoring request - otherwise looks OK.

[shamil-gadelshin]

Consider changing to task_spawner: spawn_tasks::spawn_tasks looks awkward.

[nazar-pc]

Renamed, though it is really a bad name in Substrate, I wouldn't call that function spawn_tasks in the first place.

[nazar-pc]

One more thing: this finally allows us to customize informer, which we'll extend to show Subspace networking stats in addition to Substrate networking as well as various DSN sync stages, etc.