rule: support aws_iam_policy_document_sid_required

[major0]

Support a check to require a sid in each policy statement.

[kayman-mk]

@wata727 What do you think? Seems to be an easy one.

Edit: in case heredocs are not used

[wata727]

It depends on how many people this rule is useful to. If we can't add it as a default enabled rule, a tool like OPA ruleset might be better.