Add a validate-terraform workflow to validate and lint terraform

[glennmusa]

• Adds .github/workflows/validate-terraform
• closes Pull Requests should trigger an action that validates Terraform code for syntactical correctness and style #21 runs terraform validate against all *.tf in the repository, exiting with failure if any validation should fail
• closes Pull Requests should trigger an action that validates Terraform code for syntactical correctness and style #21 runs terraform fmt -check against all *.tf in the repository, exiting with failure should any file not be formatted correctly
• closes Workflows should use the same tooling as developers #23 pulls the missionlzdev:latest container to use known tools