Add custom ping into Shredder

[tomrittervg]

Add custom ping into Shredder

[BenWu]

I'm looking at metrics.uuid.characteristics_client_identifier in the firefox_desktop.deletion_request table and there aren't any non-null values so it doesn't look like any deletion requests for this have been sent yet. @tomrittervg can you confirm if this is the right field to use for deletion requests?

It might be useful to have a deletion request to make sure we get the right fields wired up. Can you try sending one or is there a pref I can toggle to do it on my own client?

[tomrittervg]

If you set this pref to 1 (in Nightly) and then restart Firefox, you'll submit a ping. IF you disable telemetry, you should send a deletion request (AIUI.) I've just done this myself, so the deletion request should be working its way through the system, you can add yours as well.

[BenWu]

Alright I found my own deletion ping and everything looks as expected. This should be straightforward to do so I'll try to work on it in the next week

[BenWu]

The user-characteristics ping was added to shredder in #5341