* Upgrade xDS (go-control-plane) API to support Envoy 1.10.
This includes backwards compatibility shim to work around the ext_authz package rename in 1.10.
It also adds integration test support in CI for 1.10.0.
* Fix go vet complaints
* go mod vendor
* Update Envoy version info in docs
* Update website/source/docs/connect/proxies/envoy.md
* New Providers added and updated vendoring for go-discover
* Vendor.json formatted using make vendorfmt
* Docs/Agent/auto-join: Added documentation for the new providers introduced in this PR
* Updated the golang.org/x/sys/unix in the vendor directory
* Agent: TestGoDiscoverRegistration updated to reflect the addition of new providers
* Deleted terraform.tfstate from vendor.
* Deleted terraform.tfstate.backup
Deleted terraform state file artifacts from unknown runs.
* Updated x/sys/windows vendor for Windows binary compilation
Paul Banks