TODO: Add subsites integration

[sabina-talipova]

Description

There have been numerous discussions regarding Subsites integration, but there are not any PR indicating that this integration has been completed.
See: #70

If we integrate Subsites, we should set Subsite::disable_subsite_filter to true inStaticCacheFullBuildJob::getAllLivePageURLs().

[GuySartorelli]

Gonna close this since there's no other open issues related to subsites integration - Either it's working, or it's not and nobody really cares.

There's an extension hook right in that spot anyway, so arguably it would be better for a 3rd party module (or subsites itself) to implement an extension to disable the subsite filter at that point, rather than having this module be coupled to subsites.