Add support for Pendo Track events and Page/Feature events

[chriszarate]

Description

Provide Pendo-based telemetry in two main parts:

• Server-to-server Pendo "Track events" are conceptually similar to Automattic Tracks events, but have a different payload structure. Usage is almost identical to that of Automattic Tracks.
• Client-side Pendo Page/Feature events require a client library to be enqueued and configured. Moved to Implement Pendo JavaScript library (Page/Feature events) #6150

See an explanation of "Event types" on this page.

In general, I've tried to follow the 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:

• PENDO_TRACK_SECRET_KEY: The secret integration key used to authenticate with Pendo and send Track events.
• PENDO_SNIPPET_API_KEY: The (non-secret) client API key used to configure Pendo's JavaScript library.
• VIP_DISABLE_PENDO_TELEMETRY: If true, prevents the JavaScript library from being enqueued. Server-to-server Pendo Track events are still sent.
• VIP_SF_ACCOUNT_ID: The account ID added to event payloads and used to correlate Pendo events.

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

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 10 lines in your changes missing coverage. Please review.

Project coverage is 30.94%. Comparing base (50d93d8) to head (dd01619).

Files with missing lines	Patch %	Lines
telemetry/pendo/class-pendo-track-client.php	84.61%	6 Missing ⚠️
telemetry/pendo/pendo-utils.php	93.10%	2 Missing ⚠️
telemetry/class-telemetry.php	92.30%	1 Missing ⚠️
telemetry/pendo/class-pendo.php	97.29%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #6140      +/-   ##
=============================================
+ Coverage      30.41%   30.94%   +0.53%     
- Complexity      4830     4878      +48     
=============================================
  Files            290      296       +6     
  Lines          21327    21489     +162     
=============================================
+ Hits            6486     6650     +164     
+ Misses         14841    14839       -2     

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[sonarqubecloud]

Quality Gate passed

Issues
5 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