Add new module for Azure NAT gateway

[andreadecorte]

SUMMARY

Gateway association with subnets to be handled in the subnet instance.
Add relevant integration tests.
I added a default value for SKU for consistency. REST API doesn't have a default value.
I took inspiration from the existing modules for handling of resources IDs.
Support for Public IP prefixes is not implemented, it can be done in a second time.

Fixes #794

ISSUE TYPE

• New Module Pull Request

COMPONENT NAME

Azure NAT Gataway

ADDITIONAL INFORMATION

[alfwed]

Many thanks for this PR !
It would be great to also be able to specify the Public IP to associate with the gateway. My company is using a naming convention for every resource and although we badly need this module, we wouldn't be able to use it as it is because of the lack of the public IP option. Any chance you could add it too?

[andreadecorte]

This is the case, you will be able to specify one or more existing public IP addresses as parameter for the NAT gateway. Unless you meant to use public IP prefixes, and this is indeed not included, as it required an additional new module, but it can come later

[alfwed]

Sorry I wasn't looking at the right module file. It looks perfectly fine to me 👍

[xuzhang3]

@andreadecorte LGTM