Replace VALUE_OPTIONAL with VALUE_DEFAULT in get_chapters_parameters()

[vithushau]

This issue addresses a bug where the VALUE_OPTIONAL parameter in the get_chapters_parameters() function was causing errors during unit testing.

core\externallib_test::test_all_external_info with data set "pulseaction_notification_get_chapters" (stdClass Object (...))
Unexpected debugging() call detected.
Debugging: External function parameters: invalid OPTIONAL value specified.
* line 730 of /lib/externallib.php: call to debugging()

To resolve this issue, VALUE_OPTIONAL has been replaced with VALUE_DEFAULT, ensuring that the parameter remains optional while providing a default value when omitted.

Additionally, this issue includes the addition of missing privacy providers.

Moodle Version: 4.1.10