feat: add ability to set global properties

Not all properties can be set globally, and the "appName" in the global case is currently defaulted to `--global`. This is okay because domain label names cannot start with hyphens, and all app names must be valid domain label names.

plugins/network/network.go

@@ -22,6 +22,9 @@ var (
 		"attach-post-deploy":  "",
 		"tld":                 "",
 	}
+
+	// GlobalProperties is a map of all valid global network properties
+	GlobalProperties = map[string]bool{}
 )
 
 // BuildConfig builds network config files