The DebugConfig in the self endpoint can change at any time. It's not a stable API.
With the previous change to rename GRPCPort to XDSPort this command would have broken.
This commit adds the XDSPort to a stable part of the XDS api, and changes the envoy command to read
this new field.
It includes support for the old API as well, in case a newer CLI is used with an older API, and
adds a test for both cases.
Daniel Nephin