Implement override_enable_notifications.

Refs #4746
Implement override_enable_flapping.

Refs #4746
Implement override_enable_perfdata.

Refs #4746
Implement override_event_command.

Refs #4746
Implement override_check_command.

Refs #4746
Implement override_max_check_attempts.

Refs #4746
Implement override_check_period.

Refs #4746
Update documentation.

Refs #4746
Merge branch 'feature/modified-attributes-4746' into next

Fixes #4746