Migrate attribution pixel to pixel kit

[alessandroboron]

Task/Issue URL: https://app.asana.com/0/0/1207002879349167/f

Description:
Migrates the Installation Attribution Pixel to use PixelKit.

Steps to test this PR:

Download the Review App here
Make sure to clean up the app's data directory by running sh clean-app.sh review.
Run the App.
Search for pixel:m.mac.install in Kibana.

Extra:
Create the Origin.txt file manually and add it to the Bundle of the App (.app/Contents/Resources) to test that the pixel fires and has the origin field set.
This requires to re-sign the App again in order to run it.
Steps to re-sign the App here

In terminal:

codesign -d --entitlements :- DuckDuckGo.app > entitlements.plist
Copy result of security find-certificate -a -c "Developer ID Application" -Z | grep ^SHA-1 | cut -d " " -f3 | uniq
Code sign the App using the below:
--force
--sign <paste value generated from #2 here>
--options runtime
--entitlements entitlements.plist
--generate-entitlement-der “DuckDuckGo.app”
Once the App is re-signed you need to open it by right-click on the icon and select Open from the context menu otherwise you won’t be able to open it.

---

Internal references:

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

[github-actions]

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[alessandroboron]

I had to change the frequency to standard. I couldn’t find a way to make the pixel fire again when testing.

This function

public func pixelLastFireDate(pixelName: String) -> Date? {
        var date = defaults.object(forKey: userDefaultsKeyName(forPixelName: pixelName)) as? Date
        if date == nil {
            date = defaults.object(forKey: legacyUserDefaultsKeyName(forPixelName: pixelName)) as? Date
        }
        return date
    }

returned a date even though I'd clean the App state with the clean-app.sh script.

Technically this is still safe because in StatisticsLoader we check the condition of statisticsStore.hasInstallStatistics. If this is false we fire the pixel otherwise we return. So it would fire only once per installation.

func load(completion: @escaping Completion = {}) {
        if statisticsStore.hasInstallStatistics {
            completion()
            return
        }

        requestInstallStatistics(completion: completion)
    }

where hasInstallStatistics is

var hasInstallStatistics: Bool {
       return atb != nil
}

var atb: String? {
       get {
           pixelDataStore.value(forKey: Keys.atb)
       }
       set {
           if let value = newValue {
               pixelDataStore.set(value, forKey: Keys.atb)
           } else {
               assertionFailure("Unexpected ATB removal")
               pixelDataStore.removeValue(forKey: Keys.atb)
           }
       }
   }

[federicocappelli]

Understood thanks, PixelKit for now it lacks a function for cleaning up the UserDefaults used for that dates, I'm going to implement it before opening the PR

[federicocappelli]

LGTM, I'll add a task for re-testing this after I have implemented a "reset" function for Pixelkit's data storage