Send success pixel on successful data import

[graeme]

Task/Issue URL: https://app.asana.com/0/1203822806345703/1207768516988587/f

Description:

During ✓ Postmortem: Deduplicate passwords on import it was mentioned that having insight on the rate of import success vs failure would be useful.

We already have Pixels for failures but cannot calculate a success rate from that alone.

This adds import success Pixels with source and make sure the failure Pixels and their source parameter are being sent properly.

Steps to test this PR:

1. Run this with the debugger attached
2. Perform password / bookmark / favicon imports from all the import sources (or at least a sensible subset)
3. Check that, on successful import, the pixel: m_mac_data-import-succeeded_{action}_{source} is sent

Definition of Done:

• Does this PR satisfy our Definition of Done?

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Internal references:

Pull Request Review Checklist
Software Engineering Expectations
Technical Design Template
Pull Request Documentation

[amddg44]

Tested out a whole bunch of imports and LGTM!

One small note, from the list of action cases bookmarks, passwords, favicons, generic I wasn’t able to trigger any bookmarks or passwords actions even when selecting import via html / csv file but perhaps I missed an import flow

[github-actions]

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