chore(nat-gateway): Add nat_gateway_tags_per_az variable for NAT gateways

[pavlospt]

Description

Adding nat_gateway_tags_per_az variable for NAT gateways

Motivation and Context

It is useful for cost related reports to be able to tag NAT gateways per AZ.

Breaking Changes

No

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects
• I have executed pre-commit run -a on my pull request

[pavlospt]

@bryantbiggs @antonbabenko Sorry for tagging you directly, but would it be possible to have a review here? 🙏🏻

[bryantbiggs]

why is this a useful change, what motivates a specific tag per NAT?

[pavlospt]

@bryantbiggs Extremely useful for cost observability reasons (at least in our case, we can know what volume of traffic is going through each of our NATs and correlate that with the workloads living there, by using Cost Reports with Tag dimension).

[bryantbiggs]

but you know the NAT gateway IDs and can use that to correlate, no? this sounds like a side effect of cross-AZ traffic which I don't see the benefit of taking on such complexity in this module for this peculiar case

[pavlospt]

By using common tags across resources we can do what I describe above. I am not sure why or how this feature brings the complexity you mention, given that the info we need is already there and we just utilize it.

Indeed it made things pretty clear for us regarding Cross AZ traffic costs. If you have better alternatives to suggest, we would love to investigate them!