Initial xDS Server Design and Implementation

[danehans]

#16 specifies the need for an xDS server to configure managed Envoy instances. The xDS server details should be captured in this issue or a linked doc.

[arkodg]

related #16 (comment) & #16 (comment)

[arkodg]

@youngnick raised #70 so we can track the auth + authz implementation for gRPC communication b/w Envoy proxy and the xDS Server which should ensure that the xDS server can trust different data plane components / envoy proxies deployed by the provisioner allowing the default Envoy Gateway implementation to be based off a single binary (i.e. the Provisioner can deploy unique data planes and the xDS Server can push different xDS resources to different data planes ). A single binary should help simplify installation and operations, which is also something the Istio community realized after running multiple control plane sub components in a cluster.

[danehans]

@LukeShu I assigned this issue to you based on the 5/24/22 community meeting notes. Please unassign yourself if that's not the case.

[danehans]

Per #60, this issue should use incremental instead of stow xds.