Expose gateway's external information and interfaces

[an0rak-dev]

Description

• expose gateway's external information
• expose gateway's interfaces
• fix a mapping issue in the REST response of a gateway's external information

This is done to implement this todo.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] Improvement (improve existing resource(s) or datasource(s))
• [x] Documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Run locally using my own OVH public cloud account.

Test Configuration:

• Terraform version: terraform version: Terraform v1.8.2
• Existing HCL configuration you used:

  
  resource "ovh_cloud_project_network_private" "priv_net" {
      service_name = var.ovh_project_number
      name = "private_network"
      regions = ["GRA11", "RBX-A"]
  }

resource "ovh_cloud_project_network_private_subnet" "priv_subnet" { service_name = var.ovh_project_number network_id = ovh_cloud_project_network_private.priv_net.id dhcp = true region = "GRA11" start = "12.0.0.2" end = "12.0.0.254" network = "12.0.0.0/24" no_gateway = false }

resource "ovh_cloud_project_gateway" "subnet_gateway" { service_name = var.ovh_project_number name = "gateway-GRA11" model = "m" region = "GRA11" network_id = ovh_cloud_project_network_private.priv_net.regions_attributes[0].openstackid subnet_id = ovh_cloud_project_network_private_subnet.priv_subnet.id }

# Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings or issues
- [x] I have added acceptance tests that prove my fix is effective or that my feature works
- [x] New and existing acceptance tests pass locally with my changes
- [x] I ran succesfully `go mod vendor` if I added or modify `go.mod` file