A way to enforce transaction order in a block

[xlc]

Previous discussion: paritytech/substrate#4177

Is it possible enforce certain transaction to be included in the beginning of the block? Or more generalized version, enforce transaction orders in a block.

A deterministic transaction order (e.g. order by their hash) reduces the ability for block author to manipulate the block in their favor. Block author won't be able to arbitrarily craft and insert transaction to gain advantages. They can still to do this in some degree but at least it will be harder.

Use case: I would like to enforce oracle transactions to always be included in the beginning of the block to reduce the possibility of front-running. By doing this, block producer will not able to craft and insert buy transaction before oracle price update and sell transaction after price update and making profit risk-free. With honest block producer that includes all received transactions, front runner will not able to monitor price change and make arbitrage because price update transaction is more likely to be executed before his arbitrage transaction.

[kianenigma]

will be done as a part of #198