Fix vpn connection setup while tunnel cidr is used

[ppieprzycki]

Hello,

I'd like to propose two changes

• As I tried to use tunnel CIDR in my VPN setup I had a problem with creating an "aws_vpn_resource".
  This module tries creating both resources named "default" and "tunnel" for the same IPsec connection.
  Fix makes sure that the "Default" resource is not created when any of var.tunnel* variables are set.

• The second change introduces new variable named "create_vpn_gateway_attachment".
  Idea behind is to not create an association between vGW and VPC within this module
  The other module "terraform-aws-vpc" already has logic that is responsible for creating vGW and attaching it to a VPC.
  Also, a problem arises when we configure two VPN connections and we want later delete one of them (or we have direct connect). If we delete vgw attachment we cannot further use other connection.
  The new variable is set by default to true to provide backward compatibility.

[antonbabenko]

@miguelaferreira What do you think about all this?

[miguelaferreira]

The contribution in this PR is very welcome.

I've made a few comments with proposals for small adjustments to the code, and it looks overall good to me.

I've also tested the PR and got the expected results:

Apply complete! Resources: 46 added, 0 changed, 0 destroyed.

Outputs:

vpn_gateway.vpn_connection_id = vpn-0ed0e25583f2e89ce
vpn_gateway.vpn_connection_tunnel1_address = 34.247.237.2
vpn_gateway.vpn_connection_tunnel1_cgw_inside_address = 169.254.33.90
vpn_gateway.vpn_connection_tunnel1_vgw_inside_address = 169.254.33.89
vpn_gateway.vpn_connection_tunnel2_address = 54.229.206.2
vpn_gateway.vpn_connection_tunnel2_cgw_inside_address = 169.254.33.102
vpn_gateway.vpn_connection_tunnel2_vgw_inside_address = 169.254.33.101
vpn_gateway2.vpn_connection_id = vpn-058bd8b96b511877f
vpn_gateway2.vpn_connection_tunnel1_address = 34.240.59.142
vpn_gateway2.vpn_connection_tunnel1_cgw_inside_address = 169.254.34.102
vpn_gateway2.vpn_connection_tunnel1_vgw_inside_address = 169.254.34.101
vpn_gateway2.vpn_connection_tunnel2_address = 52.18.208.78
vpn_gateway2.vpn_connection_tunnel2_cgw_inside_address = 169.254.34.90
vpn_gateway2.vpn_connection_tunnel2_vgw_inside_address = 169.254.34.89

Thanks

[ppieprzycki]

Hi
Thanks for reviewing. I've made suggested changes. Please check if they seem good.

[miguelaferreira]

Thanks a lot for the effort @ppieprzycki 👍

@antonbabenko LGTM

[antonbabenko]

You guys ROCK! 🥇

v1.5.0 has been released.

[github-actions]

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