Fix/assets benchmarks

[JuaniRios]

What?

• Fix pallet-assets benchmarks

Why?

• We need to compute our runtime weights

How?

• The create benchmark was trying to create an asset with id 0, and we used that for DOT. We know use 10 for DOT

Testing?

just dry-run-benchmarks

Anything Else?

When we set up prices for assets, we should refer to the id's not directly, but through the AcceptedFundingAsset.to_assethub_id() interface. Fixed that in mock