Installing gettext RPM

In order to work with yaml files for kubernetes deployments we need
a tool to do variable substitutions.
Usually we would use `yq` but Azure Linux is not packaging this binary
the next best thing is envsubst which is provided by the gettext rpm.

Author: naioja

linux/base.Dockerfile

@@ -135,7 +135,8 @@ RUN bash ./tdnfinstall.sh \
   terraform \
   gh \
   redis \
-  cpio
+  cpio \
+  gettext
 
 # Install azure-functions-core-tools
 RUN wget -nv -O Azure.Functions.Cli.zip `curl -fSsL https://api.github.com/repos/Azure/azure-functions-core-tools/releases/latest | grep "url.*linux-x64" | grep -v "sha2" | cut -d '"' -f4` \