Merge branch 'tf-security-documentation' into 'master'

Update terraform documentation

See merge request gitlab-org/gitlab!39902

doc/user/infrastructure/index.md

@@ -190,6 +190,12 @@ and the CI YAML file:
 
 The output from the above `terraform` commands should be viewable in the job logs.
 
+CAUTION: **Caution:**
+Like any other job artifact, Terraform plan data is [viewable by anyone with Guest access](../permissions.md) to the repository.
+Neither Terraform nor GitLab encrypts the plan file by default. If your Terraform plan
+includes sensitive data such as passwords, access tokens, or certificates, GitLab strongly
+recommends encrypting plan output or modifying the project visibility settings.
+
 ## Example project
 
 See [this reference project](https://gitlab.com/nicholasklick/gitlab-terraform-aws) using GitLab and Terraform to deploy a basic AWS EC2 within a custom VPC.