This PR fixes a bug in the edges command where if src_resources from two
different namespaces sent requests to the same dst_resource, the original
src_identity was overwritten.
Adds a check to Prometheus `edges` queries to verify that data for the requested
resource type exists. Previously, if Prometheus could not find request data for the
requested resource type, it would skip that label and still return data for
other labels in the `by` clause, leading to an incorrect response.
This change adds an endpoint to the public API to allow us to query Prometheus for edge data, in order to display identity information for connections between Linkerd proxies. This PR only includes changes to the controller and protobuf.
Carol A. Scott