Update the gcp_envoy_bootstrap.json to use correct label for looking up mesh-name (#37551)
Update the gcp_envoy_bootstrap.json to use correct label for looking up mesh-name (#37551)

* Changes to make pilot-agent generate correct bootstrap to connect to GCP
TrafficDirector

The changes in the PR fall in two categories
1) bootstrap template (gcp_envoy_bootstrap.json)
  - Change to support the new xDS V3 nodeID format used by
  TrafficDirector
  - Change to explictly support V3 API when connecting to
  TrafficDirector
  - Changes to support istio-proxy inbound interception.

2) supporting changes in pilot-agent to set bootstrap template
varaibles.

cla: yes

* Pass the metadata.Labels to the bootstrap template and change
gcp_envoy_bootstrap file to use information to generate correct NodeId

* Pass the metadata instead of just label to the template.

Also, update the gcp_envoy_bootstrap label lookup from "gke.io/mesh" to "td.io/scope"

* Remove the metadata entries for TRAFFICDIRECTOR_ as this will come from
sidecar injector

* Update the gcp_envoy_bootstrap.json to use correct label for looking up
mesh-name
istio/istio,istio/istio,istio/istio,istio/istio,istio/istio