Introduce BASEFEE opcode

[begmaroman]

Description

Introduce BASEFEE opcode

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

[igorcrevar]

minor objection but otherwise looks good

Edit: I have already approved but then I realized that tests are failing. I think you need to enable opcode only if London fork is enabled:

func opBaseFee(c *state) {
    if !c.config.London {
        c.exit(errOpCodeNotFound)

        return
    }

    baseFee := big.NewInt(0).Set(c.host.GetTxContext().BaseFee)
    c.push1().SetUint64(baseFee.Uint64())
}