Adding required environment variable rules logic.

[matajoh]

If an environment variable rule is marked as "required", then it must be defined in the container. This is enforced in the Rego in the following way:

env_ok(pattern, "string", value) {
    pattern == value
}

env_ok(pattern, "re2", value) {
    regex.match(pattern, value)
}

rule_ok(rule, env) {
    not rule.required
}

rule_ok(rule, env) {
    rule.required
    env_ok(rule.pattern, rule.strategy, env)
}

envList_ok(container) {
    every env in input.envList {
        some rule in container.env_rules
        env_ok(rule.pattern, rule.strategy, env)
    }

    every rule in container.env_rules {
        some env in input.envList
        rule_ok(rule, env)
    }
}

Signed-off-by: Matthew A Johnson matjoh@microsoft.com