Reading list import logging

[tonisevener]

Phabricator:
https://phabricator.wikimedia.org/T322805

Notes

This PR adds the event logging for importing shared reading lists.

Test Steps

1. Fresh install an app, then toggle on logging either via the onboarding flow or app Settings.
2. Inspect traffic via a proxy, look for traffic with MobileWikiAppiOSReadingLists in the url.
3. Trigger the reading list import modal by visiting the landing page in Safari.
4. Via proxy, confirm you see an event call with category: shared, action: receive_start, and measure: 8 (the number of articles that are shared in this particular landing page link).
5. Tap X. Confirm you see an event with category: shared and action: receive_cancel
6. Repeat step 3, then tap Create reading list button. Confirm you see an event with category: shared, action: receive_finish, and measure: 8.
7. Wait until survey appears on the reading list detail screen. Confirm you see an event with category: shared, action: survey_shown.
8. Tap the take survey button. Confirm you see an event with category: shared, action: survey_clicked.

[mazevedofs]

Working great!