Send local GRANDPA authority id to telemetry (#3646)

* Fix indentation

There is a space between the tabs.

* Send local GRANDPA authority id to telemetry

* Update core/finality-grandpa/src/lib.rs

Co-Authored-By: Bastian Köcher <[email protected]>

* Generalize authority_id()

* Shorten code

* Do not send unfinalized authority sets to telemetry

`update_authority_set()` is called from, among others,
import side. These updates only track a pending change
and may or may not happen, hence it's wrong to send
this set to telemetry (which would assume that this is
the current, finalized authority set).

* Send current authority set and local authority id on set change