refactor: move all port management code to standalone ports plugin

This change makes interacting with port mappings more clear - folks might previously set the port mapping to the proxy type or vice-versa.

The existing proxy:ports* commands still exist but will show a deprecation warning for a single minor release.

plugins/ports/proxy.go

@@ -0,0 +1,21 @@
+package ports
+
+import (
+	"fmt"
+)
+
+// PortMap is a struct that contains a scheme:host-port:container-port mapping
+type PortMap struct {
+	ContainerPort int
+	HostPort      int
+	Scheme        string
+}
+
+func (p PortMap) String() string {
+	return fmt.Sprintf("%s:%d:%d", p.Scheme, p.HostPort, p.ContainerPort)
+}
+
+// AllowsPersistence returns true if the port map is not to be persisted
+func (p PortMap) AllowsPersistence() bool {
+	return p.Scheme == "__internal__"
+}