add evaluation window to rate based statement

[dremesa]

When creating waf rules with a rate-based-statement, I'd like for the ability to control the evaluation window, right now it defaults to the aws value of 300 seconds, and I'd like to be able to set the other values if needed. Right now I have to do so manually in the aws console.

    rule
        name: "RateLimit"
        priority: 7
        action: "BLOCK"

        visibility-config
            metric-name: "ratelimit"
            cloud-watch-metrics-enabled: true
            sampled-requests-enabled: true
        end

        statement
            rate-based-statement
                limit: 750
            end
        end
    end