Include connected accounts in tracks from the backend.

[mikkamp]

Changes proposed in this Pull Request:

This PR adds any connected accounts to tracks which we send from the backend. The accounts are only included if they are connected (non-zero).

Detailed test instructions:

There aren't a lot of tracks being sent from the backend to test with, so I added the following line to ConnectionTest::render_admin_page:

do_action( 'woocommerce_gla_url_switch_success', [] );

1. Make the change (suggested above) to add the manual track
2. Browse a site with both MC and Ads accounts connected
3. Turn on browser developer tools and browse to the hidden connection page: https://domain.test/wp-admin/admin.php?page=connection-test-admin-page
4. In the browser developer tools filter network requests to pixel.wp.com
5. Look for a request for t.gif and check the payload
   
6. Confirm that gla_version, gla_ads_id, gla_merchant_id all reflect the right values

Changelog entry

• Add - Include connected accounts in tracks from the backend.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (a91fa6c) 59.4% compared to head (d82b62b) 59.5%.

Additional details and impacted files

@@             Coverage Diff             @@
##             develop   #2198     +/-   ##
===========================================
+ Coverage       59.4%   59.5%   +0.1%     
- Complexity      4127    4129      +2     
===========================================
  Files            453     453             
  Lines          16478   16482      +4     
===========================================
+ Hits            9788    9807     +19     
+ Misses          6690    6675     -15     

Flag	Coverage Δ
php-unit-tests	59.5% <50.0%> (+0.1%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/Tracking/Tracks.php	69.2% <50.0%> (-8.5%)	⬇️

... and 2 files with indirect coverage changes

[martynmjones]

Hey @mikkamp, thanks for the tracks adjustment.

Confirmed that gla_version, gla_ads_id, and gla_merchant_id values are all included in the payload and values are correct so LGTM ✅