Implement `pallet-asset-rewards` (#3926)

Closes #3149 

## Description

This PR introduces `pallet-asset-rewards`, which allows accounts to be
rewarded for freezing `fungible` tokens. The motivation for creating
this pallet is to allow incentivising LPs.

See the pallet docs for more info about the pallet.

## Runtime changes

The pallet has been added to
- `asset-hub-rococo`
- `asset-hub-westend`

The `NativeAndAssets` `fungibles` Union did not contain `PoolAssets`, so
it has been renamed `NativeAndNonPoolAssets`

A new `fungibles` Union `NativeAndAllAssets` was created to encompass
all assets and the native token.

## TODO
- [x] Emulation tests
- [x] Fill in Freeze logic (blocked
https://github.com/paritytech/polkadot-sdk/issues/3342) and re-run
benchmarks

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Co-authored-by: command-bot <>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: muharem <ismailov.m.h@gmail.com>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>