Customized resource type extension support

[neverhook]

trafficstars

Currently there is limited count of resource types in xDSv2/xDSv3, and should be enough for common scenarios.

But if we have some customized resource types, e.g. private module in envoy which relies on specific configs, then resource type extension support is needed.

Like that the pattern UDPA suggests: separate transport(UDPA-TP) and data-models(UDPA-DM), and it should be easy to extend data models.

[jakubdyszkiewicz]

I like the idea, I think go-control-plane introduced support for it recently.

Sample use case: in Kuma we built communication between control planes using xDS.

[slonka]

Right now there are no plans to work on this feature, if you have time feel free to post a more detailed proposal so we can discuss the implementation.