Fix telemetry span not entering properly & enter span in sc-cli (#7951)

* WIP

* WIP

* Test

* bug fix

* WIP

* Revert "WIP"

This reverts commit 4e51e9adfdf0dc7cf37b562b60a0e83ca1d0b00d.

* doc

* Improve comment on why all spans are preserved

* Added missing suggestion from previous PR

* Use BoxFuture

* Move TelemetrySpan creation to sc-cli, need to test...

* Test code

* Adapt user code

* Revert "Test code"

This reverts commit 333806b2fe1626efaa2691f9f44d0b4dd979bc36.

* Update client/service/src/task_manager/mod.rs

Co-authored-by: David <[email protected]>

* Better & simpler solution

Co-authored-by: David <[email protected]>