impl Debug for sc_service::Configuration (#6400)

* Initial commit

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* Make sc_service::Configuration derive Debug

* Replace task_executor fn's input by proper TaskExecutor type (cleaner)

* impl From<Fn> for TaskExecutor

* Update client/cli/src/runner.rs

* Add some doc, examples and tests

* Replace Deref by fn spawn as suggested

Co-authored-by: Bastian Köcher <[email protected]>