gitignore: don't check in terraform secrets
gitignore: don't check in terraform secrets

[skip ci]

phnmnl/mantl,datascienceinc/mantl,mantl/mantl,phnmnl/mantl,KaGeN101/mantl,ContainerSolutions/microservices-infrastructure,mantl/mantl,bitium/mantl,ContainerSolutions/microservices-infrastructure,CiscoCloud/mantl,sehqlr/mantl,CiscoCloud/mantl,CiscoCloud/microservices-infrastructure,CiscoCloud/microservices-infrastructure,sehqlr/mantl,bitium/mantl,datascienceinc/mantl,KaGeN101/mantl