Implement foreign asset transaction fees

[Chralt98]

To integrate asset fee payment for the front end, see this:

• https://substrate.stackexchange.com/questions/5695/informing-polkadot-api-about-additional-signed-extensions
• https://substrate.stackexchange.com/questions/8063/where-do-i-add-a-signedextension-in-a-subxt-call
• https://github.com/polkadot-js/api/blob/8ba4ed53776a7a71478e229547c7af3d4dc57d63/packages/types/src/extrinsic/signedExtensions/statemint.ts#L7-L14
• https://github.com/paritytech/substrate/blob/5ea6d95309aaccfa399c5f72e5a14a4b7c6c4ca1/frame/transaction-payment/asset-tx-payment/src/lib.rs#L141-L152

Also see this:

• Extension to Treasury Pallet for Assets paritytech/polkadot-sdk#92
• https://docs.rs/pallet-asset-tx-payment/latest/src/pallet_asset_tx_payment/lib.rs.html#32-34
• https://github.com/paritytech/substrate/blob/85415fb3a452dba12ff564e6b093048eed4c5aad/frame/treasury/src/lib.rs#L618-L627 treasury does not work with multiple currencies

Follow up PR:

Use an actual swap with a liquidity pool from substrate to convert foreign into native token and then pay the fees with the following substrate functionality:

https://github.com/paritytech/substrate/tree/master/frame/asset-conversion

https://github.com/paritytech/substrate/blob/master/frame/transaction-payment/asset-conversion-tx-payment

[codecov-commenter]

Codecov Report

Merging #1022 (5c028e0) into main (31b7d64) will decrease coverage by 1.58%.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##             main    paritytech/substrate#1022      +/-   ##
==========================================
- Coverage   94.50%   92.93%   -1.58%     
==========================================
  Files          92       92              
  Lines       21070    21589     +519     
==========================================
+ Hits        19913    20064     +151     
- Misses       1157     1525     +368     

Flag	Coverage Δ
tests	92.93% <ø> (-1.58%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 21 files with indirect coverage changes

[sea212]

Please also update docs/changelog_for_devs.md

[sea212]

debug_assert! would be useful here to know when funds are just lost.

[Chralt98]

true, 5c028e0