Introduces a new `UDPOriginProxy` interface and `UDPOriginService`
to standardize how UDP connections are dialed to origins. Allows for
future overrides of the ingress service for specific dial destinations.
Simplifies dependency injection for UDP dialing throughout both datagram
v2 and v3 by using the same ingress service. Previous invocations called
into a DialUDP function in the ingress package that was a light
wrapper over `net.DialUDP`. Now a reference is passed into both datagram
controllers that allows more control over the DialUDP method.
Closes TUN-9469
b4a98b13fe