Add support for Pendo Track events

[chriszarate]

Description

Provide telemetry for Pendo "Track events." These events are conceptually similar to Automattic Tracks events, but have a different payload structure. See an explanation of "Event types" on this page.

Usage is almost identical to that of Automattic Tracks. This PR introduces a generic Telemetry class that will send events to both Automattic Tracks and Pendo. Going forward, we will update our plugins to use the Telemetry class.

In general, I've tried to follow the implementation pattern provided by the existing Tracks implementation and the generic Telemetry base classes and interfaces. I did make some minor changes to the abstract class Telemetry_Event and the extending Tracks_Event class in order to improve the abstraction and reduce code duplication.

New constants will need to be provided in order to configure this functionality automatically:

• VIP_PENDO_TRACK_INTEGRATION_KEY: The integration API key used to authenticate with Pendo and send Track events. This key can only be used to write (append) events to Pendo's API.
• VIP_SF_ACCOUNT_ID: The account ID added to event payloads and used to correlate Pendo events.

Note

Client-side Pendo Page/Feature events has moved to #6150

Pre-review checklist

Please make sure the items below have been covered before requesting a review:

• This change works and has been tested locally or in Codespaces (or has an appropriate fallback).
• This change works and has been tested on a sandbox.
• This change has relevant unit tests (if applicable).
• This change uses a rollout method to ease with deployment (if applicable - especially for large scale actions that require writes).
• This change has relevant documentation additions / updates (if applicable).
• I've created a changelog description that aligns with the provided examples.

Pre-deploy checklist

• VIP staff: Ensure any alerts added/updated conform to internal standards (see internal documentation).

Steps to Test

1. Check out PR.
2. Follow README to use the Telemetry class and record events.

[codecov]

Codecov Report

Attention: Patch coverage is 97.53695% with 5 lines in your changes missing coverage. Please review.

Project coverage is 30.99%. Comparing base (74d2acf) to head (436d377).

Files with missing lines	Patch %	Lines
telemetry/pendo/pendo-utils.php	93.10%	2 Missing ⚠️
telemetry/class-telemetry-client.php	0.00%	1 Missing ⚠️
telemetry/class-telemetry.php	92.30%	1 Missing ⚠️
telemetry/pendo/class-pendo.php	97.50%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #6140      +/-   ##
=============================================
+ Coverage      30.42%   30.99%   +0.57%     
- Complexity      4826     4875      +49     
=============================================
  Files            290      296       +6     
  Lines          21329    21495     +166     
=============================================
+ Hits            6489     6663     +174     
+ Misses         14840    14832       -8     

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[sonarqubecloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[chriszarate]

I've added guards against requiring missing files during rollout in 436d377. There are no external consumers of these files, so nothing to guard on the usage side.