* Add Tproxy support to Envoy Extensions (this is needed for service to service validation)
* Add validation for Envoy configuration for an upstream service
* Use both /config_dump and /cluster to validate Envoy configuration
This is because of a bug in Envoy where the EndpointsConfigDump does not
include a cluster_name, making it impossible to match an endpoint to
verify it exists.
This removes endpoints support for builtin extensions since only the
validate plugin was using it, and it is no longer used. It also removes
test cases for endpoint validation. Endpoints validation now only occurs
in the top level test from config_dump and clusters json files.
Co-authored-by: Eric <eric@haberkorn.co>
