Optimism local testnet setup

[Lohann]

Feature description
Create a rust crate at chains/optimism/testing/... that manages a local Optimism testnet, below an example of what is expected:

obs: this is just an example, feel free to remove/add fields from those structures as necessary.

/// All settings necessary to configure an arbitrum testnet
pub struct Config {
    /// Base Directory for store temporary files (chain config files, docker volumes, etc).
    pub base_directory: PathBuf;
   
    /// Port where the L2 Optimism node is listening, if none pick a random port
    pub optimism_port: Option<u16>,

    /// Port where the L1 ethereum node is listening, if none pick a random port
    pub ethereum_port: Option<u16>,
    
    /// unlocked accounts which will receive funds.
    pub main_account: Vec<(ethereum_types::Address, ethereum_types::U256)>,
    
    // ...
}

pub struct OptimismEnv {
    // ...
}

impl OptimismEnv {
    /// Starts a new optimism testnet
    pub async new(config: Config) -> Result<Self>;
    
    /// Stop the optimism testnet and cleanup dependencies
    /// ex: stop docker containers, delete temporary files, etc
    pub async cleanup(self) -> Result<()>;
}

Related

This library will be used by the new testing framework: #158

Expected output

• it correctly starts a new optimism network
• it correctly cleanup the optimism network
• Multiple optimism networks can be created simultaneously as long there's no port conflicts.
• Unit tests covering all basic functionalities