feat: Add custom inflation calculation

[arijitAD]

Description

1. The Akash whitepaper defines a time-based function for the inflation: I(t). The way cosmos-sdk currently calculates inflation is different as compared to what the Akash whitepaper prescribes. So, we need the cosmos-sdk to accept a custom function to calculate inflation. When the custom function isn't provided, it should use the default inflation calculation logic as it currently does.

2. The inflation function defined in the Akash whitepaper does not account for the inflation range that is an important piece of cosmos inflation mechanics. It is proposed that we add a chain parameter for deriving a range from I(t). Let's call the chain parameter R. It will be a percentage of I(t). So from I(t), we can get a range [I(t) - I(t) * R, I(t) + I(t) * R], and then we can input that range as min, max inflation parameters of the current inflation mechanics.

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[arijitAD]

1. The Akash whitepaper defines a time-based function for the inflation: I(t). The way cosmos-sdk currently calculates inflation is different as compared to what the Akash whitepaper prescribes. So, we need the cosmos-sdk to accept a custom function to calculate inflation. When the custom function isn't provided, it should use the default inflation calculation logic as it currently does.

This part is done in this PR.

2. The inflation function defined in the Akash whitepaper does not account for the inflation range that is an important piece of cosmos inflation mechanics. It is proposed that we add a chain parameter for deriving a range from I(t). Let's call the chain parameter R. It will be a percentage of I(t). So from I(t), we can get a range [I(t) - I(t) * R, I(t) + I(t) * R], and then we can input that range as min, max inflation parameters of the current inflation mechanics.

I think, instead of defining a parameter in the cosmos-sdk's mint module, we can create a separate subspace in our app for storing such extra parameters and use them in the custom inflation calculator function, which will again be defined in our code. The reason is that this particular parameter is very specific to our way of calculating the inflation and doesn't seem fit to be included in the sdk for generic purposes.

[boz]

Looks great - thanks for the light touch on the upstream repo 🚀

[boz]

Can minter.NextInflationRate() be turned into a types.InflationCalculationFn function so that it can be the default?

[arijitAD]

Done

[boz]

Looks great! Thank you @arijitAD

[arijitAD]

Added PR in origin cosmos#10441