Download all Posts from a Saved Collection

Provide us a use case of the feature instaloader --login=your_username :saved:COLLECTIONNAME

Describe the solution you'd like Instead of blanket downloading all saved items, could we create way to download only one collection? This would make it easier to organize saved files.

Describe alternatives you've considered N/A

If the feature request is accepted, would you be willing to submit a PR? Unfortunately I don't have the wherewithal to program this atm

Additional context Reopening #166 2yrs later

(please also see https://instaloader.github.io/contributing.html for how to suggest a feature)