Synchronizer VS disabled subscriptions

Environment

Reproduced in any environment

How to reproduce

• subscribe to some list
• (optional) wait until next synchronization, check filters are downloaded
• unsubscribe from the list
• wait until disabled subscription expires, check it is not downloaded

Observed behavior

Disabled subscription will be downloaded after it is disabled

Expected behavior

It should not be downloaded.

Requirements

We agreed with @Quiri that HEAD requests should have a higher frequency (5 days by default, we'd like to make it 1 day instead), as these are virtually byte-less request,s but a higher frequency would help us having better metrics regarding subscriptions.

We also agreed that the subscription lastVersion should be updated, through the Date response header, whenever a HEAD request is successful, so that we know when it is that the user checked for subscriptions state, and provide better support when subscriptions are re-enabled (both metrics and downloads).