Add support for custom logging field

[maskit]

This adds a new TS API, TSLogFieldRegister, which I proposed on the list.

[bneradt]

[approve ci autest 1]

[Copilot]

Pull request overview

This pull request adds support for custom logging fields in Apache Traffic Server, allowing plugins to register new log fields or replace existing ones. The implementation introduces a new lifecycle hook TS_LIFECYCLE_LOG_INITIALIZED_HOOK that fires after the logging system initializes but before the logging configuration loads, giving plugins an opportunity to register custom fields.

Changes:

• Introduces a new lifecycle hook and event for log field customization
• Adds public API functions for registering custom log fields and helper marshal/unmarshal functions
• Refactors logging initialization to separate field initialization from configuration loading
• Provides a complete example plugin demonstrating the feature

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 14 comments.

Show a summary per file

File	Description
src/traffic_server/traffic_server.cc	Invokes the new lifecycle hook after logging initialization but before config loading
src/proxy/logging/LogField.cc	Adds constructor for custom fields and updates marshal/unmarshal logic
include/proxy/logging/LogField.h	Defines CustomMarshalFunc and CustomUnmarshalFunc types
src/proxy/logging/LogAccess.cc	Implements custom field marshaling wrapper
src/proxy/logging/Log.cc	Separates field initialization from config loading by introducing load_config()
src/api/InkAPI.cc	Implements TSLogFieldRegister and helper marshal/unmarshal functions
include/ts/ts.h	Declares public API functions
include/ts/apidefs.h.in	Adds lifecycle hook/event enums and TSLogType enum
example/plugins/c-api/custom_logfield/custom_logfield.cc	Example plugin demonstrating custom log field usage
example/plugins/c-api/CMakeLists.txt	Adds custom_logfield plugin to build
doc/developer-guide/api/types/TSEvent.en.rst	Documents new lifecycle event
doc/developer-guide/api/functions/TSLifecycleHookAdd.en.rst	Documents new lifecycle hook
doc/developer-guide/api/functions/TSLogFieldRegister.en.rst	Comprehensive API documentation for custom log fields