Implement oracle price coefficient in DB for gas_adjuster

[thomas-nguy]

In complement to this proposal

matter-labs/era-contracts#15

We need to multiply the gas_adjuster by a coefficient so that the gas price can reflect the price of the base token

This PR do the following

• Create a new value in DB called gas_token_adjust_coefficient that an external oracle can update
• The gas adjuster will fetch this value in DB and multiple the gas price with this coefficient in estimate_effective_gas_price
• Default value is 1 so it is a non breaking change

[mm-zk]

does it always fetch the latest one? Or do we assume that this table has only 1 value?

[popzxc]

Hello! First, thanks for the contribution. Second, sorry for the review taking so long -- we're still getting used to being open-source.

We're currently working on improving the modularity of zkSync so that it's more suitable for different zkStack use cases.
The new shape of the code will come with the ability to replace components like GasAdjuster with custom implementations.
Once this is implemented, it will be possible to implement the proposed changes without altering the core codebase.

Given that currently there are a lot of projects with different expectations regarding zkStack node capabilities, we believe that this approach will work better at scale than trying to change the core codebase to adjust to all the possible use cases.

So, unfortunately, right now we won't be merging this change, but we promise that soon you will be able to get the desired behavior (and maybe introduce even more features) using the newly provided APIs.