docs: fix broken links

### Terraform integration in Merge Requests

This template enables [Terraform integration in Merge Requests](https://docs.gitlab.com/ee/user/infrastructure/mr_integration.html).

This template enables [Terraform integration in Merge Requests](https://docs.gitlab.com/ee/user/infrastructure/iac/mr_integration.html).

As a result if you enabled your `production` environment, every merge request will compute and display infrastructure changes compared to `master` branch.

#### GitLab managed Terraform State (default)

By default, this template enables [GitLab managed Terraform State](https://docs.gitlab.com/ee/user/infrastructure/terraform_state.html).

By default, this template enables [GitLab managed Terraform State](https://docs.gitlab.com/ee/user/infrastructure/iac/terraform_state.html).

[As mentionned in GitLab's documentation](https://docs.gitlab.com/ee/user/infrastructure/iac/terraform_state.html#initialize-a-terraform-state-as-a-backend-by-using-gitlab-cicd),

that requires that your Terraform scripts declare the (unconfigured)

| Name                     | description                            | default value     |

| ------------------------ | -------------------------------------- | ----------------- |

| `TF_IMAGE`               | the Docker image used to run Terraform CLI commands <br/>:warning: **set the version required by your project** | `registry.hub.docker.com/hashicorp/terraform:latest` |

| `TF_GITLAB_BACKEND_DISABLED`| Set to `true` to disable [GitLab managed Terraform State](https://docs.gitlab.com/ee/user/infrastructure/terraform_state.html) | _none_ (enabled) |

| `TF_GITLAB_BACKEND_DISABLED`| Set to `true` to disable [GitLab managed Terraform State](https://docs.gitlab.com/ee/user/infrastructure/iac/terraform_state.html) | _none_ (enabled) |

| `TF_PROJECT_DIR`         | Terraform project root directory        | `.`               |

| `TF_SCRIPTS_DIR`         | Terraform (hook) scripts base directory (relative to `$TF_PROJECT_DIR`) | `.` |

| `TF_OUTPUT_DIR`          | Terraform output directory (relative to `$TF_PROJECT_DIR`). Everything generated in this directory will be kept as job artifacts. | `tf-output` |

    {

      "name": "TF_GITLAB_BACKEND_DISABLED",

      "type": "boolean",

      "description": "Set to disable [GitLab managed Terraform State](https://docs.gitlab.com/ee/user/infrastructure/terraform_state.html)",

      "description": "Set to disable [GitLab managed Terraform State](https://docs.gitlab.com/ee/user/infrastructure/iac/terraform_state.html)",

      "advanced": true

    },

    {