Implement search term logging and analytics

[adalcima]

Description

This PR adds logging for site search by combining Wagtail search_promotions module with a local SearchEvent model.

Related issue: TP1-3913
Review app: https://foundation-s-tp1-3913-i-fgoydx.mofostaging.net/cms/

Note: Follow up tickets will be created as mentioned in the ticket.

Main changes

• Added searchpromotions native module to enable basic logging of search queries.
• Added a SearchEvent model to extend the logic of searchpromotions module and store: query_string, language, results_count, created_at fields. With this model, we can record searches that yield no results.
• Updated search view to log on initial search submit (both searchpromotions and SearchEvent logs).

How to test:

1. Visit the search page and try different terms.
2. Log in to the review app and verify that there's a new report under Reports -> Search terms, which displays the search terms and a hit counter. Explore the options to filter and generate a CSV or XLSX file.
3. Also, check that a new Promoted search result setting has been added. This can be populated with popular terms from the new Search Promotions module.
4. A new search_searchevent table is storing additional data. For now, we are only storing records.
   Credentials to connect to the Heroku DB are available here

Images

• Search termsn report

- Promoted search results setting - SearchEvent DB model

[danielfmiranda]

Wow! Very cool @adalcima this will definitely be useful in the future. Thanks for taking this on. Looks good to me! Approved 👍