Add legacy client id in deletion request ping in Glean

[daoshengmu]

Is your feature request related to a problem? Please describe.
Per the request from Glean team, we need to add this delete request ping for the transition of moving out our legacy telemetry.

Describe the solution you'd like
The ping is like the document mentioned. Add it in the metrics.yaml and call legacy_client_id.set(TelemetryHolder.get().getClientId() ) before Glean.Initialize().