[FR]: CLI parameter to update desired feeds

[blackwaterpark22]

Brief description of the feature request

Hello there, I wanted to suggest a potential feature that is similar to the CLI url parameter for adding new feeds like the example in https://rssguard.readthedocs.io/en/stable/features/cli.html but for updating feeds instead

Instead of adding the whole URL for each feed, I imagine the easiest way this could be done is with the Item IDs and (I don't know if they exist) maybe Category IDs?

rssguard.exe -fetch_all
rssguard.exe -fetch_category "1, 4"
rssguard.exe -fetch_item "20, 45, 110, 140, etc"

The use case for this would be for more restrictive feeds that blocks/timeouts the user if too many connections are requested, so they can set a batch command using the task scheduler to only update those problematic feeds in the desired interval since it is not feasible for everyone to keep their computers running until the next scheduled feed update of let's say, 48 hours. It also just gives more options to the user overall