[update documentation] custom cron expressions for harbor_interrogation_services

[tomfankhaenel]

Current state
The Interrogation Services can be configured to use preconfigured schedules like described here

It can also use custom cron expressions like in the UI and API but it is not mentioned in the documentation.

Request
It would be very good to know this feature is implemented in case you need a more specific cron expression or at a different time during the day.

[wrighbr]

@tomfankhaenel I actually think it accepts a cron string for argument vulnerability_scan_policy. But it's just not documented.

[tomfankhaenel]

@tomfankhaenel I actually think it accepts a cron string for argument vulnerability_scan_policy. But it's just not documented.

I should have tested this first :D Thanks, it worked as described.
In that case the request would be to add this feature to the description ;)