Document Gas Price Algorithm

[MitchTurner]

Part of #1624

We are going to land on a gas price algorithm that has its own set of parameters and configuration. This should be documented well so that it is easy to audit and maintain.

[MitchTurner]

https://www.notion.so/fuellabs/How-is-the-Gas-Price-calculated-on-Fuel-17c2f2293f3180f5b4baf71729592b46?pvs=4

[AurelienFT]

I read it and this document is very interesting but it shouldn't leave on notion only for us I think. We could add it to the public docs (https://docs.fuel.network/) for anyone to understanding our fee model, maybe under "Specifications" section. (Maybe remove the last section if it goes there)