Issue #3628657: Add configurable activity logging

Problem/Motivation

Activity records are currently always written to the Drupal system log. On busy sites, this creates unnecessary watchdog entries and can also send activity records to external logging backends.

Proposed resolution

Add a configuration option to control whether activity records are also written to the Drupal system log.

The setting:

• Adds a checkbox to the Activities settings form.
• Defaults to the existing behavior of logging activity records.
• Allows administrators to disable system logging while activity records continue to be stored normally.
• Adds an update hook to preserve the existing enabled behavior for existing installations.
• Adds a Kernel test covering the configuration behavior.

Testing

Manually verified that:

• Activity records are created when system logging is enabled.
• Activity records continue to be created when system logging is disabled.
• The activities watchdog entry is created when enabled.
• The activities watchdog entry is not created when disabled.
• Existing Drupal logging continues to work normally.