Add documentation on how to disable/enable vulnerability detection in the Manager

[MARCOSD4]

Description

After talking to @Rebits, we think it would be useful to include in the Vulnerability Detection module documentation specific information on how to disable/enable vulnerability detection in the manager with the vulnerability-detection.disable_scan_manager option in the internal_options.conf file, as there is currently no mention of this.

In addition, it should take into account what has been reported in this issue.