@stanley-cheung noticed a bug where CSM labels were not being added on
metrics if the peer was not also CSM Observability enabled.
This PR fixes the behavior to add in the local labels in this case, as
well as add the remote workload type label with the value of unknown.
Changes -
* Remove `csm.remote_workload_pod_name` and
`csm.remote_workload_container_name`.
* Add `csm.remote_workload_name`, the value for which is sent through
MetadataExchange, from the `CSM_WORKLOAD_NAME` env var. (Note that this
is not added in local labels.)
* Add a local `csm.canonical_service` (@markdroth, please verify the key
that we want here) that is read from `CSM_CANONICAL_SERVICE_NAME` env
var, and we continue to send it over via MetadataExchange
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Yash Tibrewal