At the moment, users with the Manage Group Filter Subscriptions global permission are able to select any groups to be recipients of a filter subscription (source:https://confluence.atlassian.com/display/JIRA/Receiving+Search+Results+via+Email). It would be better if we can manage which groups shows up in the list in the first place.

Use Case:

1. The default jira-users group shows up in the list. Users might accidentally select this group which will "spam" all users with this filter subscription. Hiding this group will avoid such situation.
2. There might be certain groups meant for particular things which will not require to receive filter subscriptions at all so we should be able to just hide it from showing up in the first place