pallet-assets: Rename `total_supply` to `amount` (#13229)

* pallet-assets: Rename `total_supply` to `amount`

We are actually passing the `amount` on assets being minted and not the total supply.

Closes: https://github.com/paritytech/substrate/issues/13210

* ".git/.scripts/commands/fmt/fmt.sh"

* Fix compilation

* FMT

Co-authored-by: command-bot <>