Add sensei_usage_tracking_data filter hook

[m1r0]

Required by https://github.com/Automattic/sensei-pro/issues/1960, https://github.com/Automattic/sensei-pro/issues/1959, and https://github.com/Automattic/sensei-pro/issues/1958

Changes proposed in this Pull Request

• Add a usage tracking data hook, needed to allow adding more data in Sensei Pro.

Testing instructions

• There should be no logic changes. The Sensei_Usage_Tracking_Data::get_usage_data method should work as before.

New/Updated Hooks

• sensei_usage_tracking_data: Filter the usage tracking data.

[codecov]

Codecov Report

Merging #6262 (c76a091) into trunk (2c0c972) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head c76a091 differs from pull request most recent head 6c7570a. Consider uploading reports for the commit 6c7570a to get more accurate results

@@            Coverage Diff            @@
##              trunk    #6262   +/-   ##
=========================================
  Coverage     45.77%   45.78%           
  Complexity     9490     9490           
=========================================
  Files           455      455           
  Lines         33561    33562    +1     
  Branches        271      271           
=========================================
+ Hits          15363    15366    +3     
+ Misses        17996    17994    -2     
  Partials        202      202           

Impacted Files	Coverage Δ
includes/class-sensei-usage-tracking-data.php	98.22% <100.00%> (+<0.01%)	⬆️
includes/class-sensei-groups-landing-page.php	0.00% <0.00%> (ø)
includes/class-sensei-utils.php	54.21% <0.00%> (+0.10%)	⬆️
includes/class-sensei-quiz.php	60.52% <0.00%> (+0.12%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cfa81af...6c7570a. Read the comment docs.