Ensure nothing in the troubleshoot go module depends on consul's top level module. This is so we can import troubleshoot into consul-k8s and not import all of consul.
* turns troubleshoot into a go module [authored by @curtbushko]
* gets the envoy protos into the troubleshoot module [authored by @curtbushko]
* adds a new go module `envoyextensions` which has xdscommon and extensioncommon folders that both the xds package and the troubleshoot package can import
* adds testing and linting for the new go modules
* moves the unit tests in `troubleshoot/validateupstream` that depend on proxycfg/xds into the xds package, with a comment describing why those tests cannot be in the troubleshoot package
* fixes all the imports everywhere as a result of these changes
Co-authored-by: Curt Bushko <cbushko@gmail.com>
This ensures that if someone does include some extension Consul does not currently make use of, that extension is actually usable. Without linking these envoy protobufs into the main binary it can't round trip the escape hatches to send them down to envoy.
Whenenver the go-control-plane library is upgraded next we just have to re-run 'make envoy-library'.
