feat(cli): add --var shorthand for --variable (#8710)

`--variable` is used frequently enough to deserve a shorthand. Unfortunately,
`-v` is taken by verbose, and `-V` is too easily confused with version or
verbose, so we're left with "--var".

cli/templatecreate.go

@@ -170,6 +170,11 @@ func (r *RootCmd) templateCreate() *clibase.Cmd {
 			Description: "Specify a set of values for Terraform-managed variables.",
 			Value:       clibase.StringArrayOf(&variables),
 		},
+		{
+			Flag:        "var",
+			Description: "Alias of --variable.",
+			Value:       clibase.StringArrayOf(&variables),
+		},
 		{
 			Flag:        "provisioner-tag",
 			Description: "Specify a set of tags to target provisioner daemons.",