Use blockchain events to get notified for block imports

[EclesioMeloJunior]

Issue summary

• Currently in Gossamer we have the BlockchainEvents that is a new way to get notifications about client blockchains events: block imported and block finalized

Implementation details

Other information and links

• https://github.com/paritytech/polkadot-sdk/blob/21fbd6b59d37fd18a00d0ec4b6f72dc376d63010/polkadot/node/service/src/builder/mod.rs#L637

• https://github.com/paritytech/polkadot-sdk/blob/e2d3da6128bbd6a00e2036503fc2ed3e9c3c1b80/polkadot/node/overseer/src/lib.rs#L322

Acceptance criteria

[] Add AC's here..
[] Regression testing (if applicable)
[] New code is 60% covered with unit tests

[Yuri0405]

Hello @EclesioMeloJunior!
I'd like to work on issue #4810 . I did little investigation and here what I found:

• integration points: dot/core/service.go HandleBlockImport() for block imports, lib/grandpa/grandpa.go finalise() for finalization
• Discovered existing telemetry infrastructure with BlockImport and NotifyFinalized message types already implemented
• I guess core service also needs telemetry to be injected

What I would do:

• Add telemetry calls at success points in both methods

I also have few questions:

• Should I inject telemetry in core service like in grandpa.go?
• What branch should I base my PR from?

This looks pretty straightforward - mind if I give it a try?