Add support for alpine (edge) package to __consul_agent

cdist/conf/type/__consul_agent/manifest

@@ -61,6 +61,17 @@ distribution_setup () {
        user='consul'
        group='consul'
      ;;
+     alpine)
+       # consul is only available starting Alpine 3.12 (= edge during the 3.11 cycle).
+       # See https://pkgs.alpinelinux.org/packages?name=consul&branch=edge
+
+       # Override previously defined environment to match alpine packaging.
+       conf_dir='/etc/consul'
+       conf_file='server.json'
+       data_dir='/var/consul'
+       user='consul'
+       group='consul'
+     ;;
      *)
         echo "Your operating system ($os) is currently not supported with the \
           --use-distribution-package flag (${__type##*/})." >&2