[Enhancement] Add Support for Arithmetic Operations

[lizhunt-aws]

Is your feature request related to a problem? Please describe.

I'd like to do some basic math in assertions and counts() outside of the binary comparison operations.

Describe the solution you'd like

Be able to parse and validate a rule similar to the following:

let minimum_tag_ratio = 0.95
rule tag_ratio_must_be_over_sla {
    let all_resources_to_check =  Resources.*[ Type == /AWS::IAM::Role/ ]
    let found_required_tags = Resources.*[
        Type == /AWS::IAM::Role/
        Properties.Tags[*].Key == ...blahblah
        ...blah
    ]
    (count(%found_required_tags) / count(%all_resources_to_check)) >= %minimum_tag_ratio
}

[joshfried-aws]

Hey @lizhunt-aws, thanks for the suggestion. This is definitely something I could see a lot of benefit to adding. We're going to talk it over with the team and will update this ticket in the future as necessary.