Stable weights impacted by WeightToFee function

[enddynayn]

Description
Stable weights are impacted by changes in the WeightToFee function. The weight-to-fee function
uses extrinsic base weights to compute the fee. When running the benchmarks for extrinsic base weights it changes.

https://github.com/LibertyDSNP/frequency/blob/501d622245cd2f886e13a3dd4c68ca1963c2bf19/pallets/frequency-tx-payment/src/lib.rs#L298

Potential solution
Commit a weight-to-fee function for capacity.