write our own benchmarks for orml_tokens

[brenzi]

ORML unfortunately doesn't provide benchmarking logic for their pallet:
https://github.com/open-web3-stack/open-runtime-module-library/tree/v0.7.0/tokens

Acala implements them, but with a tail of Acala-dependencies
https://github.com/AcalaNetwork/Acala/blob/master/runtime/mandala/src/benchmarking/tokens.rs

best way for us is to write our own benchmarking logic, it seems

[clangenb]

I did the same for orml-vesting in ajuna: ajuna-network/ajuna-pallets#25

[clangenb]

This is the working branch for v1.10.0: ajuna-network/ajuna-pallets#45