feat: add drain_nat_ips support

[LeandroFPeixoto]

In this PR I'm including support for the field drain_nat_ips.

This functionality is very useful, when turned on, Cloud NAT IP address will be in Drain mode, meaning that the Cloud NAT IP does not accept any new connections.

Ref: https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/compute_router_nat#drain_nat_ips

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[LeandroFPeixoto]

Linked issue https://github.com/terraform-google-modules/terraform-google-cloud-nat/issues/163

[imrannayer]

@LeandroFPeixoto thx for the PR. Can you plz remove VsCode files?

[LeandroFPeixoto]

@LeandroFPeixoto thx for the PR. Can you plz remove VsCode files?

@imrannayer, done!

[imrannayer]

/gcbrun