feat: pallet asset-rate (#13608)

* poc

* fix: remove AssetIdParameter

* tests: add

* docs: add pallet description

* feat: add benches

* refactor: UnknownAssetId

* fix: normalize mock cfg

* fix: benchmarks

* chore: add weights

* refactor: remove storage getter

* chore: apply suggestions from code review

* docs: add native balance to calls

* chore: apply suggestions from code review

* chore: apply ConversionFromAssetBalance

* tests: update balance mock

* chore: apply suggestions from code review

* ci: set publish to false

* docs: fix missing rustdoc

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Co-authored-by: parity-processbot <>