[feat] Fee Handler

[stanly-johnson]

resolves #158

ToDo

• Add more docs
• Improve tests

[stanly-johnson]

@olanod I created a simple version of the pallet to get started. The next stage would be converting
fn apply_fees(from: &Account, to: &Account, asset: Asset, amount: Amount) -> Vec<(Account, Amount)>;

And within the release function to loop through all the recipients. Is that correct?
Although I think this basic version is good enough for majority of cases where we will have only one recipient of fees. The drawback of the advanced approach is that the realease extrinsic ends up being expensive for the user, even though the actual recipient count might be low, since we use the worst case in benchmark to calculate the weights which means a user always pays the transaction fee equivalent to transfer to our MAX_RECIPIENTS always. Wdyt? Should we go ahead with the Vec<> approach? 🤔

[olanod]

About the worst case scenario, it's worth doing the extra work of calculating the weight dynamically or doing a weight correction https://docs.substrate.io/v3/runtime/weights-and-fees/#dynamic-weights

[olanod]

Looks good, just a small thing :)