Pallets: Asset Rate - Rename AssetId to AssetKind, Introduce AssetKindFactory Trait (#14514)

* asset-rate rename asset_id to asset_kind

* asset-rate pallet benchmarks asset kind factory

* rename to SEED

* fixes

* Update frame/asset-rate/src/benchmarking.rs

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* sp-core optional dep

* sp-core included for benchmarks

* sp-core to dev dep

* sp-core add dep prefix

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Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>