New `root_testing` pallet (#12451)

* Move fill_block to RootOffences

* docs

* new pallet

* new line

* fix

* Update frame/root-testing/src/lib.rs

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

* Update frame/root-testing/src/lib.rs

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

* Update bin/node/runtime/src/lib.rs

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

* Update frame/root-testing/src/lib.rs

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

* Update frame/root-testing/src/lib.rs

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

* Update frame/root-testing/src/lib.rs

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

* fixes

* problem solved

* revert

* fix dependency

* hopefully making the CI happy

* ...

* dummy call

* remove dummy

* fix warning

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