decouple transaction payment and currency (#6912)

* wip: setup types

* fix types

* make tx payment pallet independent from balances

* fix dependent tests

* comments

* restructure a bit and  include more info

* clean up ugly phantom

* reduce complexity

* minor doc improvements

* use shorthand

* doc

* fix line lenght and style

* readd BalanceOf

* some clarifications and readability improvements

* move balance type to OnChargeTransaction

* remove noise

* fix style

* Apply suggestions from code review

improved documentation

Co-authored-by: Alexander Theißen <[email protected]>

* Improve naming and documentation

Apply suggestions from code review

Co-authored-by: Alexander Theißen <[email protected]>

* Apply suggestions from code review

Co-authored-by: Kian Paimani <[email protected]>

* always call withdraw_fee

* move NegativeImbalanceOf to payment module

* fix unused import

Co-authored-by: Alexander Theißen <[email protected]>
Co-authored-by: Kian Paimani <[email protected]>