Implement custom SlowAdjustingFeeUpdate in Dolphin

[ghzlatarev]

https:/paritytech/polkadot/blob/master/runtime/common/src/lib.rs#L81-L120
For starters simply copy these parameters, but eventually we want to experiment with tweaking them.
For example the AdjustmentVariable can be bumped to speed up the increase of TX fees as the network becomes more congested.
Some related PRs:
#296
#337
Some related open issues:
#343
Related doc:
https://www.notion.so/2d9269c2bb794ee0a1d05ab3ee3935ee?v=81a14d467201467280665fed9d3c32dc&p=d747e0ba3d7d49dc86c13da69d46dae8