[Spike] Update PaymentInfo to use Assets pallet for fee asset if applicable

[aidan-starke]

The problem

• At futureverse we use an asset from our Assets pallet to handle all fees for the network. The number displayed in PaymentInfo is correct, but the symbol is not, and the fee error can trigger when it shouldn't

The solution

• Add a feeAssets map in @polkadot/apps-config where any chain can add their fee asset's details
• Add a hook that attempts to fetch the fee asset balance based on that map
• If that hook finds anything, use that data for the fee error and feesForSubmission section of PaymentInfo

[aidan-starke]

@jacogr keen to get some feedback on this - I've had an idea that we could add in the module/call to the feeAssets mapping to keep the useFeeAssetBalance hook generic, i.e.

root: {
  module: "assets",
  call: "account",
  feeAsset: {
    assetId: 2,
    decimals: 6,
    symbol: 'XRP'
  }  

[evilrobot-01]

Additional hacky implementation based on Aidan's great work available at https://github.com/evilrobot-01/polkadot-js-apps for anyone interested. It still uses the static assets defined in feeAssets.ts, but adds an option to select an asset in the UI, which is then passed through via SignerOptions when sending the signed transaction.

[jacogr]

We certainly need UI support, so PRs would be appreciated for "proper" support, see #7812 (It is still going to take "some" time to get around to it)

[jacogr]

On first glance, it certainly look above-board, although very localized to a specific instance. But it moves in the right direction, so it is good.

Lemme take a proper look and pull down/play with it.