jellyseerr: fix extremely long import, run only once

cache was being invalidated for every user, and on my 5000 user test
instance, this sweated jellyseerr and my computer (audibly). Also, since
this only needs to realistically run once, a flag is set in the database
to indicate it's been done, and unset once the feature is disabled.
It'll only run on boot if the flag is unset, or if triggered by the
/tasks route. Will likely add manual trigger buttons on the web as well.

config/config-base.yaml

@@ -1407,6 +1407,7 @@ sections:
     depends_true: enabled
     description: Existing users (and those created outside jfa-go) will have their
       contact info imported to Jellyseerr.
+    deprecated: true
   - setting: constraints_note
     name: 'Unique Emails:'
     type: note