Add ConstFeeMultiplier to the transaction payment pallet

[mrshiposha]

Currently, the template node sets the FeeMultiplierUpdate of the pallet_transaction_payment::Config to the unit type.
It seems not obvious (and barely noticeable) that the default implementation of the MultiplierUpdate trait returns 0 (and not 1).
Because of that, the transaction weights will be discarded due to the multiplication by 0 inside the transaction payment pallet.

This PR suggests using the FeeMultipleUpdate equivalent to the SlowAdjustingFeeUpdate from the Polkadot runtime common.

I believe it will fix the non-obvious behavior and will add extra useful info to the template node.

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polkadot address: 11Ze4Gi9iHZ1qPEweUewWk5iUTYL4Zd18VxKZ6cHhqyrfep

[cla-bot-2021]

User @mrshiposha, please sign the CLA here.

[ggwpez]

The template node was kept simple on purpose, to not confuse new developers.
Not sure what the idea was here. Maybe @kianenigma remembers?

[kianenigma]

Yeah, this is intentional. The SlowAdjustment is a feature made for Polkadot, and I don't think we should use it in node-template.

That being said, I think the intention is to disable any weight multiplier update for node-template. This means that the default value should be set to 1, and the convert should be struct Identity. The current code is somewhat different because it basically disables any weight fee by using a multiplier that's zero.

[kianenigma]

Valid concern, but needs a different approach! I would appreciate if you fix this.

[mrshiposha]

@kianenigma maybe it would be nice to change the default implementation of the MultiplierUpdate to return 1 in the fn min()?

So the default implementation won't change the multiplier. And I will revert all the changes to the template node.
What do you think?

[ggwpez]

maybe it would be nice to change the default implementation of the MultiplierUpdate to return 1 in the fn min()?

IMO it would be better to add a new implement for the trait, since we extensively use () in testing.
Something like ConstFeeMultiplier<Get<u32>> maybe.

[kianenigma]

Thanks! Can you put a polkadot address in the description for a tip https://github.com/apps/substrate-tip-bot?

[mrshiposha]

Thanks! Can you put a polkadot address in the description for a tip https://github.com/apps/substrate-tip-bot?

Added, thank you! :)

[ggwpez]

Thanks!
CI is currently broken, but that's not your fault.

[kianenigma]

/tip small

[substrate-tip-bot]

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[ggwpez]

bot merge